THE UNIVERSITY OF ILLINOIS LIBRARY 630.7 II6b nos.as4.-4-5 co A6R1CULTURAL UIBM UNIVERSITY OF ILLINOIS Agricultural Experiment Station BULLETIN NO. 226 VARIATIONS IN FARROW: WITH SPECIAL REFERENCE TO THE BIRTH WEIGHT OF PIGS BY W. J. CARMICHAEL AND JOHN B. EICE URBANA, ILLINOIS, MAY, 1920 CONTENTS OF BULLETIN No. 226 PAGE OBJECT AND PLAN OF WORK 67 LENGTH OF GESTATION PERIOD 68 SIZE OF LITTER 71 AGE OF DAM 73 BREED 74 TIME OF YEAR 75 ORDER OF FARROWING 75 SUCCEEDING LITTERS FROM THE SAME Sow 76 SUMMARY AND CONCLUSIONS 77 INDEX TO TABLES 79 TABLES . . 80 VARIATIONS IN FARROW: WITH SPECIAL REFERENCE TO THE BIRTH WEIGHT OF PIGS BY W. J. CARMICHAEL, ASSOCIATE IN ANIMAL HUSBANDRY 1 , AND JOHN B. EICE, ASSOCIATE IN ANIMAL HUSBANDKY OBJECT AND PLAN OF WORK The object of this research has been to study the variations in farrow among the several breeds of swine, together with some of the factors other than breed that may cause noticeable differences among the litters at the time of birth. The breeding and farrowing records which have been kept in connection with the herd of swine under the management of the Ani- mal Husbandry Department of the University of Illinois, during the years 1903 to 1916 inclusive, have furnished the data for this study. These records include 720 litters containing 5,840 pigs of seven dis- tinct breeds and a number of different crosses, as well as a few litters the exact breeding of which is not definitely known. Com- plete information was not obtained in connection with every litter, but an attempt was made to secure: (a) the breeding of sire and dam; (b) age of dam; (c) length of gestation period; (d) number of pigs in the litter; (e) sex of the pigs; (f) order of farrowing; (g) individual weight of pigs; and (h) the number of pigs farrowed dead or immature. For the most part the records were kept by the herdsman actively in charge at the barns. The information contained on his records was copied into the permanent records of the office, from which the data for this study were taken. Where there was any doubt as to the accuracy of the data, it was assumed that there was no in- formation on that particular phase in connection with the litter in question. However, there has been no attempt to eliminate any litters produced by sows on any specific ration or under any par- ticular conditions, nor has there been any elimination other than that necessitated by lack of data or obvious error in the information collected. All litters farrowed in the herd within the given years have therefore been considered in this study so far as the data would permit. Individual pig weights were taken before the pigs were allowed to suckle, tested spring balance scales being used for this purpose* and the weights were recorded by pounds and tenths. In case it *Now Secretary of the National Swine Growers' Association. 67 68 BULLETIN No. 226 [May, was not possible to get the birth weights in the order of farrowing, the pigs were weighed individually as soon thereafter as possible, and the fact that the order of farrowing was not obtained was noted on the record. In some cases individual weights were not obtained because a few hours' time had elapsed before there was an opportu- nity to make such weighings. In those cases the litter weights, even tho taken, were not used for this study. The rations on which the sows were fed and the method of feed- ing and handling doubtless caused some of the variations herein- after noted. However, the rations have not been considered since the feed records are not complete for the entire number of sows nor for a sufficient number of them to make such a study of much value. The herd sows have in general been handled similar to those in many herds of pure-bred swine. A very systematic study of the field is difficult since so many factors may influence the birth weight of pigs and cause other varia- tions in connection with farrowing. Influences may so completely overlap one another that in some cases it is almost impossible to account for the variations which occur. However, the possible in- fluences considered in this study, and which will be taken up in the order named, are as follows: (1) length of gestation period; (2) size of litter; (3) age of dam; (4) breed; (5) time of year; (6) order of farrowing; (7) succeeding litters from the -same sow. The gestation period for sows is generally considered to be from 112 to 114 days, with a popular belief that the older sows will carry their litters from one to three days longer than will the gilts. Table 1 shows the relation of the age of the dam to the length of gestation period for 549 litters. Judging from these data, the general belief that older sows have a gestation period one to three days longer than younger sows seems to have no very good basis; in fact, the one-year-old sows carried their pigs slightly longer than the average for the 549 litters from Sows of all ages, which was 114.58 days from the time of service. However, it is perhaps worth noting that the average age of all sows farrowing with gestation* periods of 114 days or less was 2.24 years, while that of the sows which carried their litters 115 days or longer was 2.31 years ; which indicates that there may be a slight variation due to age. Also, many of the sows four years old or above had noticeably longer gestation periods than the average, but there were so few litters under observation among the very old sows that these differences are of doubtful significance. A variation of twenty-six days in the length of gestation is some- what longer than is expected. However, the fact that 93.6 percent 19SO] VARIATIONS IN FAKROW 69 of the litters were farrowed between the lllth and 119th days after being bred indicates that the extreme cases shown in the table are riot duplicated with very great frequency. A further study of the same distribution indicates that the date of farrow can be predicted with but reasonable accuracy since 73.8 percent of the litters were carried by the sows for periods varying from 113 to 117 days. Less than 20 percent of the litters were farrowed on the 114th day, which was the day of greatest frequency of farrow. Table 2 shows the relation of the size of litter to the length of gestation for the same 549 litters which are shown in Table 1. From this it seems that there is a tendency for some of the litters which are carried longer than the average to be smaller than would be found in a chance distribution. This is perhaps more clearly brought out in Table 3, which shows that the average number of pigs (7.6) farrowed in gestation periods longer than the average was less than the grand average number of pigs (8.00) per litter in 466 litters. Table 4 shows a very even distribution of pigs of the various birth weights according to the length of the gestation period. The heav- iest pig in the whole population of 4,115 pigs studied (4.9 pounds) was farrowed in a litter of the shortest gestation period (98 days), but this pig seemed to stand out alone, there being none other nearly so heavy. The lightest pig which was farrowed (0.2 pound) came in one of the litters farrowed on the 115th day, or near the average for the length of gestation. Aside from the two pigs to which ref- erence has just been made, and perhaps four or five others, none of which are outside of a distribution such as one would expect to find, the 4,115 pigs on which the individual weight as well as the length of gestation period was secured are very evenly centered about the 114- to 115-day gestation period and the 2.5 pounds weight per pig. The distribution of 5,188 pigs as to individual weight, which is the number regarding which individual weights were secured, is given in the graph shown on page 70. This shows a variation from 0.2 pound to 4.9 pounds, with a grand average or mean weight of 2.55 pounds and with 66.9 percent of the pigs weighing between two and three pounds. It will be noted that the greatest number of pigs usually occurs at the pound and half-pound frequencies. This is doubtless due to the fact that the scales were graduated by pounds and tenths and the pounds and half-pounds were more clearly marked than the other divisions, thus making it more natural thai the nearest pound or half-pound should be read. It is doubtful, how- ever, whether this error would noticeably alter the true average weight of the whole population, the inequalities probably balancing one another. 70 BULLETIN No. 226 [May, 42 G 1.4 1.5 1920} VARIATIONS IN FARROW 71 A study of the litters as regards the relation of breed to the length of gestation period (Table 5) reveals the fact that two breeds, Berkshire and Poland China, stand out alone as having longer gestation periods than the average for the 549 litters. The Poland Chinas carried their pigs an inappreciable fraction of a day longer than the grand average, but the Berkshires ran over more than three-fourths of a day. The fact that the Berkshires seem to have longer normal gestation periods than any other breed involved in this study, together with the fact that there were more Berkshire litters studied than litters of all other breeds combined, explains in part the reason for the grand average gestation period under con- sideration being somewhat longer in these 549 litters than is gen- erally considered to be normal. Outside of the Hampshires, of which there were but two litters, the Chester Whites had the shortest average gestation period. Following these in order of increasing gestation period are the Duroc-Jerseys, Large Yorkshires, Tarn- worths, Poland Chinas, and Berkshires. A study of the sex of the pigs in relation to the length of gesta- tion period (Table 6) shows no apparent tendency for either sex to predominate more than normal. In a majority of cases there were more males than females. Of the 4,363 pigs on which the sex as well as the gestation period was recorded, 2,074 were females and 2,289 males, or 47.5 percent females and 52.5 percent males. Table 7, showing the sex of the first and last born according to length of gestation period, indicates that there is possibly a tendency for males to predominate among the first farrowed in any given litter, and for the sex to be rather evenly distributed in the case of the last farrowed. However, from this table it is seen that in litters farrowed on the 114th day, females predominated among both the first and last farrowed, notwithstanding the fact that there were more males than females among the total number farrowed. The study of the sex of the first and last farrowed involves so few individuals that no definite conclusions can be drawn. SIZE OF LITTER The number of pigs per litter was obtained in connection with each of 720 litters containing a total of 5,840 pigs. Table 8 shows the sex of these pigs as they varied within litters of different sizes. Altho there were 183 pigs the sex of which was not obtained, a sex distribution of the remaining 5,657 is interesting and seems to in- dicate that there is a decided tendency for males to predominate, since of this number 2,933 were males and only 2,724 were females, or 51.9 percent males and 48.1 percent females. There seemed to be no noticeable correlation between the size of the litter and sex, a 72 BULLETIN No. 226 [May, predominance of males being found in a majority of different-sized litters rather than merely a tendency for this sex to predominate in those of certain sizes, either small or large. Table 9, showing the number of pigs farrowed dead or immature in the litters of different sizes, seems to indicate that there is a tendency for the larger litters to contain a larger proportion of dead or immature pigs than are found in the smaller litters, since in litters of eight pigs or less the percentage of dead or immature at birth was 7.7, whereas in the litters of more than eight pigs, 10.5 percent is the corresponding figure. Among those farrowed dead there was a greater proportion of males than females 56.0 percent males and 44.0 percent females, which is a significant difference. A study of the distribution of 5,774 pigs according to the size of the litter as well as the age of dam, as given in Table 10, indicates that sows under two years of age produce smaller litters than do sows two to four years of age. The line of averages at the bottom of the table shows a gradual increase in the size of litter as the sows grew older up to the time that they were three years old. After the sows had attained the age of three years they had a tendency to produce fewer pigs in each succeeding litter, altho the few sows which were kept until they were over five years of age seemed to maintain their fecundity better than the average even at younger ages. There was, however, at least one force operating in the herd which would tend to maintain or possibly increase the size of litter ; namely, the fact that no sows were retained in the breeding herd unless they proved to be producers either of large litters or of litters containing pigs of special worth. As a result of this selection some of the gilts which produced small litters were discarded and did not have an opportunity to exert an influence as older sows. On the other hand, this sort of selection is just what would probably be made in any herd, and the results here are therefore somewhat comparable to those which might generally be found. The distribution of 2,483 sow pigs showing the relation of the weights of the pigs to the size of the litter in which they were far- rowed (Table 11), as well as a similar distribution for the 2,705 boar pigs on which the individual weights at farrowing time were secured (Table 12), shows a marked regularity in centering around the averages. The succeeding table (Table 13) shows the same data in a form which may be more easily studied. In these comparisons the average weight of the 2,483 sow pigs is shown as 2.51 pounds and that of the 2,705 boar pigs as 2.59 pounds, the males being heavier by 0.08 pound. A study of the average weight of all pigs farrowed in litters of different sizes shows rather clearly that in litters smaller than the average (8.0 pigs) the average weight per pig (2.67 pounds) is likely to be greater than the grand average 1920] VARIATIONS IN FARROW 73 weight for all litters (2.55 pounds for the 5,188 pigs on which the individual weights were obtained). Those farrowed in litters of more than eight pigs weighed an average of 2.47 pounds each. In every case where the litter contained more pigs than the average, the average weight of all pigs in litters of that size was noticeably less than the grand average. Making a similar comparison by sex, we find that likewise the pigs of either sex in litters larger than the average have a tendency to be lighter than the average for pigs of that sex, and in litters smaller than the average the tendency is for the pigs to be heavier than the average for that sex. . AGE OF DAM Sows which are two years old or older are generally considered to be producers of larger litters and stronger pigs than are gilts or sows one and one-half years old. Table 14, showing the relation of the age of the dam to the birth weight of the pigs, indicates rather clearly that the young sowjs farrow noticeably lighter pigs than do the older mothers. The average weight of pigs from sows under two years of age was 2.44 pounds, as compared with an average weight of 2.61 pounds for the pigs from sows two years old and older. There seemed to be a fairly general increase in the weight of the pigs as the sows grew older, even until they were eight years old, altho there were so few sows over five years that the weight of the pigs from sows past maturity may not be representative. On the whole, however, the belief that the young sows produce smaller pigs is substantiated by these data. Table 10, given in connection with the discussion on the size of litters, likewise substantiates the popular belief that up to a certain age, which is about three years, there is an increase in the size of litters as the sow grows older. One frequently hears statements to the effect that even tho the older sows farrow larger litters than the gilts, they do not raise as large a percentage of the pigs farrowed because more of them are farrowed weak or dead. Table 15, in which the number of dead or immature pigs is given in litters from sows of different ages, shows that the old sows farrowed a greater percentage of dead pigs than did young dams. Eight and one-tenth percent of the pigs farrowed by sows under three years of age were dead or immature, whereas 12.3 percent (an increase of 4.2 percent) of those from dams three years or more in age were in similar condition at birth. There was, however, marked irregularity among the proportionate number ofr dead or immature at birth among the litters from sows three years old and over. There were also few litters of these classes. The sex of pigs in litters from sows of different ages (Table 16) is about as evenly distributed as it was in litters of different sizes 74 BULLETIN No. 226 [May, (Table 8) or in litters of different lengths of gestation (Table 6). It shows a uniform tendency for males to be present in slightly greater numbers than are the females. BREED Any study which can be made of the different breeds from the data available in this research cannot be conclusive because for accurate comparisons there have been too few litters from any one breed, with the possible exception of the Berkshires. At best, breed comparisons of any kind are of doubtful value and are dangerous indulgences. However, these data were collected and are given here as a possible supplement to any other which may be available at present or obtained at any future time. Table 17 shows the total number of litters of each breed in the 720 litters under observation. From this table it is evident that more Berkshire litters were far- rowed in the herd during the years that these data were being col- lected (1903-1916) than all other breeds combined. The compilation showing by breeds the average age of sows, the average length of gestation period, the number of pigs per litter, and the average weight per pig at farrowing, as pre- sented in Table 18, gives an opportunity for comparison of breeds, so far as the available material herein presented will permit. (All litters of which the breeding was not definitely known or concern- ing which there was any doubt were omitted.) The average age of the sows at the time the litters were farrowed did not vary widely, there being some sows of each breed that were kept until they were four or five years old ; consequently any varia- tion which may be found cannot logically be explained by variations in age. In the discussion in connection with Table 5 the variation in length of gestation was considered, and therefore will not be re- peated here. The largest variation which was found among the litters of the different breeds was in the size of litters, altho there was some no- ticeable variation in the weight of the pigs. Arranging the breeds according to the descending number of pigs per litter, as well as the descending weight per pig, we have the following : Pigs per litter Weight per pig Large Yorkshire 11.58 Berkshire 2.61 Chester White 9.59 Large Yorkshire 2.60 Tamworth 9.43 Chester White 2.59 Duroc-Jersey 8.74 Tamworth 2.58 Crossbred 8.00 Poland China 2.50 Berkshire 7.42 Hampshire 2.50 Hampshire 7.00 Crossbred 2.46 Poland China 6.57 Duroc-Jersey 2.25 Average 8.00 Average 2.53 VARIATIONS IN FARROW 75 In this at first there seems to be some evidence, which is con- tradictory to that found in the study of the size of the litters and its effect on the weight of the pigs, for the Large Yorkshire litters, altho they contained more pigs as an average than the average for litters, were composed of pigs which were heavier than the average. A similar statement is also true of the Chester White and Tamworth pigs. Contrary to this, we find that the Hampshire and Poland China litters, with fewer pigs than the average, had lighter pigs than the mean of the whole population. Further, it is to be noted that the Duroc-Jersey pigs weighed over one-fourth pound (0.28 pound) less than the average for all pigs. Such findings are a concrete illustration of the differences due to breeding. The foregoing tabulation shows the results of but 457 litters, the litters containing a total of 3,658 pigs, an average of 8.00 individuals per litter. The sows averaged 2.35 years in age. TIME OF YEAR The time of the year at which pigs are farrowed does not seem to exert any very noticeable influence, with any regularity, upon the length of gestation period, size of litter, or weight of pigs, altho possibly there is a tendency for larger litters and heavier pigs to occur in the months of normal farrowing seasons. This, of course, might be expected since sows farrowing in other months are, in many cases, ones which were re-bred, having been originally bred for the normal farrowing season. Such sows are doubtless somewhat abnormal. There are no positive indications that the sows will carry their litters longer during summer months than in winter, or vice versa. Summarizing here the data presented in Table 19, and arranging it by months in descending order, we have : . , Length of gestation Pigs per Weight period litter per pig July September October July April May August September March February April August September March March October October June February February August October September April June April ' May March May July June May February November July November November August November June ORDER OF FARROWING , Table 20, showing the relation of order of farrowing to sex and weight of pigs in the 261 litters on which the order of farrowing as well as the birthweight of all the pigs in the litters was ob- 76 BULLETIN No. 226 tained, indicates rather strongly that among the first farrowed, males tend to predominate more than normal, for there were 155 males to 106 females among the first born. The sex of the last farrowed was in about the normal ratio. The same table also indicates that there is a slight tendency for the first farrowed (average weight 2.60 pounds) to be heavier than the last farrowed (average weight 2.43 pounds). This is perhaps in part due to the predisposition of the males, which predominated here, to be heavier than the females. In the case of the first far- rowed here, the males averaged 2.67 pounds and the females only 2.50 pounds. There was a somewhat similar tendency for the males to predominate and to be somewhat heavier than the females, among the last farrowed, but the tendency was not so marked as among the first farrowed. SUCCEEDING LITTERS FROM THE SAME SOW In Table 21 is shown the average age, length of gestation period, number of pigs per litter, and weight of litter and pigs in succeding litters from the same sow. The gestation period of the first litter is rather consistently longer than for those following it, as was shown in Table 1. There is an increase in the number of pigs per litter in most cases until the fourth litter, at which time the sows are three to three and one- half years old. The total weight of the litter increases with each succeeding litter up to the fourth owing to the increase in the num- ber of pigs per litter as well as in the weight of the individual pigs. The age at which a sow should farrow her first litter, as well as the optimum frequency of succeeding litters, is a much debated subject. No positive conclusions can be drawn from Table 22, which gives the succeeding litters from the same sows at different ages, for there are doubtless other factors than those in the table which should be taken into consideration in determining the age at which a sow should farrow. One would infer from the first part of the table that sows farrowed their first litters at one and one-half years of age had shorter gestation periods and farrowed more and heavier pigs than sows that farrowed their first litters at one year of age. Upon studying other parts of the table, it is readily seen that con- flicting conclusions can be drawn. The sows that farrowed their first litters at one and one-half years of age rather consistently farrowed heavier pigs in the first litter than those which farrowed at one year. It is evident that other factors than the number of pigs and their size determine the age at which sows should farrow the first and succeeding litters for maximum or economical production. 19SO] VARIATIONS IN FARROW . 77 The data presented in this study are not of sufficient extent to warrant the drawing of many final conclusions. A few seem to be justified, however, and are given here in the summary, altho it must be borne in mind that even they are based on limited data. LENGTH OF GESTATION PERIOD. The records obtained from 549 litters showed a rather wide range, 98 to 124 days, in the length of gestation period, with an average of 114.58 days. However, 93.6 percent of the litters were farrowed between the lllth and 119th days, and 73.8 percent between the 113th and 117th days. Altho there may be a slight variation in length of gestation period due to age, the general belief that older sows have a gestation period one to three days longer than younger sows seems to have no very good basis. There was little, if any, correlation between the length of gesta- tion period and the birth weight of pigs, but there was a slight tendency for some of the litters which were carried longer than the average to be smaller than those which were farrowed earlier than the average. A study of the sex of the pigs in relation to the length of gesta- tion period shows no apparent tendency for either sex to predominate more than normal. SIZE OF LITTER. In this study the average size of litter was 8.1 pigs. The average weight of a litter is about 20 pounds. This weight varies almost in direct proportion to the number of pigs in the litter. In litters with fewer pigs than the average, the average weight of pigs is greater than in litters with more pigs than the average. In this study, the average weight of pigs in litters with fewer pigs than the average was 2.67 pounds, and in litters with more pigs than the average it was 2.47 pounds, while the grand average of all pigs was 2.55 pounds. There is no noticeable correlation between size of litter and sex. It is interesting to note, however, that among a total of 5,657 pigs, the sex of which was determined, 51.9 percent were males and 48.1 percent females. The predominance of males was found in a majority of different-sized litters rather than in those of certain sizes, either large or small. There is a tendency for the larger litters to contain a larger pro- portion of dead or immature pigs than are found in the smaller litters. The litters larger than the average contained 10.5 percent dead pigs, and the litters smaller than the average, 7.7 percent. The proportion of males (56.0 percent) among those farrowed dead was greater than the normal predominance of males over females. The 78 BULLETIN No. 226 [May, pigs farrowed dead or immature were decidedly lighter (2.17 pounds) than the total average weight per pig (2.55 pounds). AGE OF DAM. On the whole, the belief that young sows produce smaller pigs than do older sows is substantiated by these data. Like- wise the data substantiate the popular belief that up to a certain age, which is about three years, there is an increase in the size of litter as the sows grow older. In this study the average number of pigs from sows one and one and one-half years old was 7.5, and from sows two years old or older 8.6, with average weights of 2.44 pounds and 2.61 pounds respectively. The older sows farrowed a greater percentage of dead or imma- ture pigs than did the younger sows. Out of a total of 5,778 pigs, 8.1 percent of those farrowed by sows one to two and one-half years old were dead or immature, while 12.3 percent of those farrowed by sows three years old or over were farrowed dead or immature. A study of the sex of pigs from sows of different ages showed a uniform tendency for males to be present in slightly greater. numbers without relation to the age of the sow. BREED. There are rather wide differences among different breeds as to the length of gestation, size of litter, and birth weight of pigs. Berkshires had appreciably longer gestation periods (115.4 days) than did any of the other breeds. TIME OF YEAR. It is very doubtful whether there are any varia- tions in farrow which can be attributed to the season at which the pigs are farrowed. ORDER OF FARROWING. Of the first farrowed, the proportion of males (59.4 percent) was greater than the normal ratio of males to females. The sex of the last farrowed (51.0 percent males) was in about the normal ratio. In comparing the averages of the same sex, as well as the averages of both sexes, it was found that the average weight of the first farrowed was somewhat heavier than the average of the last farrowed. SUCCEEDING LITTERS FROM THE SAME Sow. There was an increase in the number of pigs per litter and in the weight of individual pigs in most cases until the fourth litter, at which time the sows were three to three and one-half years old. The data compiled in an attempt to throw light upon the much debated subject of the age at which a sow should farrow her first litter, as well as the optimum frequency of succeeding litters, is decidedly conflicting. It would seem that other factors than the number of pigs and their size should determine the age at which sows should farrow the first and succeeding litters for maximum or economical production. 19SSO'] VARIATIONS IN FARROW 79 INDEX TO TABLES PAGE 1 Eelation of Age of Dam to Length of Gestation Period 80 2 Kelation of Size of Litter to Length of Gestation Period 81 3 Eelation of Length of Gestation Period to : (a) Size of Litter (b) Number of Pigs Farrowed Dead or Immature (c) Weight of Litter (d) Weight of Pigs 82 4 Eelation of Length of Gestation Period to Birth Weights of Pigs 83 5 Eelation of Breed to Length of Gestation Period 84 6 Eelation of Length of Gestation Period to Sex of Pigs 85 7 Eelation of Length of Gestation Period to Sex of Pigs Farrowed First and Last in the Litter 85 8 Eelation of Size of Litter to Sex of Pigs 86 9 Eelation of Size of Litter to Number of Pigs Farrowed Dead or Immature . 86 10 Eelation of Size of Litter to Age of Dam 87 11 Eelation of Weight of Pigs to Size of Litter in Which Farrowed: Females 88 12 Eelation of Weight of Pigs to Size of Litter in Which Farrowed : Males 89 13 Eelation of Weight of Pigs to Size of Litter in Which Farrowed: Males and Females 90 14 Eelation of Age of Dam to Birth Weight of Pigs 90 15 Eelation of Age of Dam to Number of Pigs Farrowed Dead or Immature. 91 16 Eelation of Age of Dam to Sex of Pigs 91 17 Total Number of Litters of Each Breed 91 18 Eelation of Breeding to: (a) Age of Dam (b) Length of Gestation Period (c) Size of Litter (d) Weight of Litter (e) Weight of Pigs 92 19 Eelation of Month of Farrowing to: (a) Age of Dam (b) Length of Gestation Period (c) Size of Litter (d) Weight of Litter (e) Weight of Pigs 92 20 Eelation of Order of Farrowing to Sex and Weights of Pigs 93 21 Data Concerning Succeeding Litters from the Same Sows 94 22 Data Concerning Succeeding Litters from the Same Sows at Different Ages 95 SO BULLETIN No. 226 [May, W i & I > J 1.9 SS853SS83e3SS883 fc^-2 3 ~- S;*! 3322^22232 2 2 2 IN c>i 00 IO CO IO IN CO M CO I rH | | | | rji oo (N CO 00 co IN |s 1 I 10 (NrH(NrH (N Oi CO rH IN .2 fl 3 OlOrHrHOOl 1 COIN 1 CM 1 1 rH IN IN IN rHrH 3 IN H- s .a co rH 00 00 00 IN CO CO rH | rH | | | | CO 10 - CO CN >> ji 3 J (N ^l"CNrH^4|COICO|rH| | rH CO oi g 3 CO CO CO CO rH rH IN 1 1 1 1 1 1 1 CD IN T3 .a 5 IN IN rH rH (N rH IN 1 1 1 1 rH | | S ei i cc rHrH | 1 1 1 1 I 1 1 1 1 1 1 0) ! 1 *53 jz rH | | | rHrH I 1 1 1 1 ! 1 1 CO o IO M t c rHrHrH | 1 1 1 1 1 | 1 1 1 1 CO S _a CO 1 rH | | | | | | | | | | | | rt S | IN O 1 1 rH , | | | | | | | | | | rt 8 0) Is CO 05 a IN 8 CO . MO 2^S ill 1 5^ fta k Flli < 10 fl -i O 11 9.4 la l rH 3 O o a Q.IO li ii as s i 5S 82; SPC 111 0^5 3 5!.a 19X01 VARIATIONS IN FARROW 81 .,-1 . .p . ..H IH iH 1H IO CO rH CO U5 IN t- -iHINf-liHi-li-ICOCONr-l r-< N i-H T-I N IN N feS - fl a- 9 82 BULLETIN No. 226 [May, TABLE 3. RELATION OP LENGTH OP GESTATION PERIOD TO: (a) SIZE OP LITTER, (b) NUMBER OP PIGS FARROWED DEAD OR IMMATURE, (c) WEIGHT OP LITTER, AND (d) WEIGHT OP PIGS Length of gestation period, days Num- ber of litters Total number of pigs Average number of pigs per litter Pigs farrowed dead or immature Average weight per litter, Ibs. Average weight per pig, Ibs. Number Percent 98.. 2 1 1 3 3 2 10 13 39 60 88 80 84 42 23 8 3 2 1 1 16 9 10 27 16 15 71 112 329 544 725 611 648 338 157 63 24 5 10 9 8.0 9.0 10.0 9.0 5.3 7.5 7.1 8.6 8.4 9.1 8.2 7.6 7.7 8.0 6.8 7.9 8.0 2.5 10.0 9.0 'i 1 '3 13 7 25 37 57 45 45 23 19 4 1 io!6 3.7 26!6 18.3 6.3 7.6 6.8 7.9 7.4 6.9 6.8 12.1 6.3 4.2 26.1 20.4 27.9 20.6 13.8 18.8 17.4 21.4 21.2 22.8 20.3 19.7 19.8 20.5 18.5 21.1 18.2 7.9 22.4 20.2 3.26 2.27 2.79 2.29 2.58 2.51 2.45 2.48 2.51 2.51 2.46 2.59 2.57 2.55 2.71 2.68 2.28 3.14 2.24 2.24 102 103 106 107 108 110 Ill 112 113 114 115 116 117 118 119 120 121 123 124 Total or average. . 466 3739 8.0 281 7.5 20.3 2.54 Farrowed on or before the 114th day 222 244 1874 1865 8.4 7.6 144 137 7.7 7.3 21.0 19.7 2.49 2.58 Farrowed after the 114th day 19X0} VARIATIONS IN FARROW 83 t^O irHCOCOCOOOOO 'COCO'*OOOCOCOrHCOCOOCOrHt^.cOCOI--t~a>iOC IN (N CO CO Tj< t^ t- 00 rH t- * K5 CO iH Oi O * IN CO 00 IN IN CO I I I I I I I I CO I * O 5 CO O CO t~. 00 S I INrH I I I rH I I rH rH rH rH CO (N (N CO C<5 * * CO U5 O rH (N CO * "5 CO t>- 00 OS O rH M CO * C3> 84 BULLETIN No. 226 [May, I H O oS = ** MOC10JOCINCOO O>C<5 ** CO * 9 " : ' 1920] VARIATIONS IN FARROW 85 TABLE 6. RELATION OP LENGTH OF GESTATION PERIOD TO SEX OF PIGS Length of gestation period, days Sex of pigs Number of pigs in these litters, sex of which was not obtained Total number of pigs studied Female Male 98.. . 10 4 3 10 6 9 34 59 177 314 427 339 334 202 81 36 15 3 3 8 6 5 7 17 10 6 46 81 210 298 446 370 404 211 106 35 14 2 9 6 ie> 4 4 9 17 6 24 15 9 1 3 'e 16 9 10 27 16 15 96 156 391 621 890 715 762 428 196 72 32 5 18 14 102 103 106 107 108 110 Ill 112 113 114 115 116 117 118 119 120 121 123 124 Total 2074 45 2289 63 114 4477 Percent 47.5 52.5 Number farrowed on or be- fore the 114th day 1053 1021 1132 1157 50 64 2235 2242 Number farrowed after the 114th day TABLE 7. RELATION OF LENGTH OF GESTATION PERIOD TO SEX OF PIGS FARROWED FIRST AND LAST IN THE LiTTER 1 Length of gestation period, days FIRST FABBOWED LAST FARROWED Sows Boars Sows Boars 106. . . 1 '4 12 13 29 15 19 12 a 2 'i 1 '5 4 8 16 19 31 30 11 9 1 2 1 2 1 1 1 1 'i 3 9 17 25 18 22 4 4 1 2 1 '4 4 10 10 15 24 19 17 10 1 'i 1 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 123 124 Total 112 142 110 116 Percent of each sex .... 44.1 55.9 48.7 51.3 Number farrowed on or before the 114th day.. . Number farrowed after the 114th dav... 59 53 54 88 58 52 43 ' 73 'In some cases the sex of the last farrowed was not secured, owing either to absence of attend- ant or to the fact that it was not possible to determine the sex. 86 BULLETIN No. 226 [May, TABLE 8. RELATION OF SIZE OF LITTER TO SEX OF PIGS Number of pigs per litter Number of pigs of each sex Number ofpigs, sex of which was not obtained Total number studied Females Males I... 2 15 30 97 137 195 255 374 331 449 292 237 149 101 29 11 8 12 4 15 27 82 157 213 347 397 329 442 326 226 179 105 45 21 ' 10 8 'i 11 12 21 13 24 19 20 17 10 18 1 16 6 30 57 180 305 420 623 784 684 910 638 480 338 224 75 48 18 20 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 20 Total 2724 2933 183 5840 Percent of each sex 48.1 51.9 Number in litters of 8 pigs or less 1105 1619 1242 1691 2405 3435 Number in litters of more than 8 pigs TABLE 9. RELATION OF SIZE OF LITTER TO NUMBER OF PIGS FARROWED DEAD OR IMMATURE Number of pigs per litter Pigs farrowed dead or immature Number of litters Total number of pigs Females Males Totali Percent 1... 1 'i 3 7 14 8 26 18 25 30 30 23 24 6 2 1 2 2 1 4 4 17 26 25 66 42 63 60 69 53 55 44 3 5 3 5 16.6 13.3 7.0 9.4 8.5 6.0 10.6 5.4 9.2 6.6 10.8 11.0 16.3 19.6 4.0 10.4 16.7 25.0 6 15 19 45 61 70 89 98 76 91 58 40 26 16 5 3 1 1 6 30 57 180 305 420 623 784 684 910 638 480 338 224 75 48 18 20 2 3 1 9 8 7 19 13 13 18 19 20 21 20 4 5 6 7 8 9 10 11 12 13 14 15 16 4 1 3 18 20 Total 177 225 5451 9.3 720 5840 Percent 44 56 Number in litters of 8 pigs or less . 58 119 80 145 185 360 7.7 10.5 403 317 2397 3435 Number in litters of more than 8 pigs 'The sex of some of the dead pigs and of some of those that were immature was not obtained. NOTE. 9.3 percent of the pigs, or 1.3 pigs per litter, were farrowed dead or immature. The average weight of the pigs farrowed dead or immature in 720 litters was 2.17 pounds. VARIATIONS IN FARROW 87 TABLE 10. RELATION OF SIZE OF LITTER TO AGE OF DAM Number of pigs per litter Age of dam, years Total number of litters 1 1H 2 2K 3 sy 2 4 4M 5 5H 6 6^ 7 8 1 X 9 5 15 18 43 61 68 87 96 75 91 57 40 26 16 5 3 1 1 2 4 7 13 20 14 22 23 21 17 11 4 2 1 3 2 10 11 17 13 24 17 15 8 9 3 2 2 1 7 12 12 13 19 10 21 3 10 7 6 3 2 2 4 8 8 11 9 11 9 6 4 1 2 1 '"3 4 4 7 5 4 4 5 2 2 1 3 ... 1 6 3 5 7 4 7 6 13 4 6 4 i 2 3 5 8 2 5 4 4 1 3 1 3 4 5 1 1 3 4 2 2 2 1 1 6 7 "i 1 2 1 3 1 1 1 8 g 1 1 10 6 1 1 1 2 2 1 i i 2 11 12 13 14 1 15 3 16 1 1 1 18 1 20 1 Total 162 134 126 80 68 40 43 22 15 5 7 4 1 1 708 Average number of nigs oer litter 7 ?, 7 9 8 4 8 6 9 3 8 fi 8 4 8 ?, 7 1 10 6 8 9 7 8 7 7 NOTE. The 708 litters contained 5,774 pigs, an average of 8.1 pigs per litter. The average number of pigs from sows 1 and 1% years old was 7.5 pigs. The average number of pigs from sows 2 years old or over was 8.6 pigs. BULLETIN No. 226 [May, TABLE 11. RELATION OP WEIGHT OP PIGS TO SIZE OP LITTER IN WHICH FARROWED: Females Weight per P.JS. 26s. Number of pigs per litter Total number of litters 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 18 20 .7. . 1 1 2 1 4 5 3 13 10 19 26 26 46 56 . 53 65 80 149 100 126 158 158 209 156 163 170 93 187 80 80 60 53 55 28 20 10 4 7 2 5 1 1 1 1 2483 8 . .. 1 1 1 1 ?, .9 .. 1 1 o 1 2 1 8 8 5 3 5 8 7 23 20 23 26 22 24 17 13 24 6 21 5 7 10 7 4 3 4 5 1 2 1 7 13 7 8 14 16 25 18 15 30 26 31 35 30 22 11 33 12 10 7 7 5 2 4 2 2 1 3 2 2 5 9 9 8 19 14 20 18 18 34 22 18 16 15 15 3 1 7 3 7 2 3 2 1 3 1 7 8 8 6 10 14 14 13 13 12 19 9 12 16 7 15 10 13 5 5 1 2 1 1 1 2 1 2 9 3 6 4 10 1 4 10 5 9 5 8 6 9 7 4 5 2 2 .... 1 1.1 1 1 1.2 1 1 1 1 1 5 "i 2 6 1 4 3 6 3 11 9 12 16 9 14 13 7 18 7 7 5 4 5 6 1 1 2 2 2 5 6 4 7 9 17 4 11 8 17 19 16 15 20 10 16 10 9 6 2 5 1 3 3 1 1 1 "S '"e 5 6 8 11 16 15 7 21 20 29 22 25 23 11 29 13 17 9 11 10 2 4 4 2 3 2 3 3 1 3 8 4 9 5 6 11 6 7 2 1 4 2 3 1 1.3 14 1.5 1 1 1 "3 3 "i i 2 1 1 1 3 1 3 2 1.6 1 1 4 1 2 4 1 1.7 1 "i 1 1 1.8 19 1 1 2 1 5 2.0 a "2 i 2.1 2 "l "i 2.2 1 6 8 5 4 6 3 2 5 3 1 1 2 7 6 5 1 1 1 2 7 8 5 5 10 13 9 18 6 5 2 2 5 1 4 3 1 2 3 2.4 2.5 1 1 "2 3 3 1 1 5 1 2 1 2 2 2 1 "i 2 1 i "i i "i 2 2.6 2.7 i S 2.8 29. 3.0 l 2 "2 i 1 3.1 3.2 3 3 1 1 2 i 34 3.5 3 i 3.6 3 7 3 8 1 1 2 1 39. 1 2 4.0 1 V 1 4.1 1 4 2 1 1 2 1 4 3 1 4 4 1 4.5 1 4.9 1 2 125 Total 13 30 80 177 238 327 309 400 278 234 121 M 21 11 s 12 Percent weighing 2 . 5 pounds or less '. 52 . 6 Percent weighing over 2 . 5 pounds 47.4 The females constituted 47 . 9 percent of the total number of pigs farrowed. 1980] VARIATIONS IN FARROW 89 TABLE 12. RELATION OF WEIGHT OP PIGS TO SIZE OP LITTER IN WHICH FARROWED: Males Weight per r8- /6s. Number of pigs per litter Total number of litters 1 2 8 4 6 7 8 9 10 11 12 13 14 15 16 18 20 .2 1 1 1 2 4 2 19 13 16 14 29 42 36 48 77 73 132 104 136 150 158 213 171 171 172 132 231 108 97 80 71 67 36 28 26 12 16 6 4 4 2 1 .4 1 .7. . , 9, 8 1 1 1 1 1 1 .9 1 1 3 2 3 1 3 8 3 4 10 7 16 13 16 16 21 22 15 24 24 11 35 18 12 10 15 8 6 4 3 ' "2 1 1 4 1 3 3 5 6 6 7 11 8 21 11 14 15 25 22 21 16 14 15 25 10 8 11 6 6 3 1 3 ri 1 2 4 '"2 5 7 6 6 10 14 16 14 22 18 16 32 23 36 34 18 33 14 7 14 9 14 6 6 8 4 3 1 5 1 1 1 2 6 6 9 9 12 13 10 21 21 21 25 16 22 25 11 26 19 10 5 4 4 1 2 : Vi ''" 1 1 2 2 2 5 2 4 7 10 6 20 13 15 14 10 18 14 3 8 12 17 7 6 5 7 6 5 2 2 1 1 '"2 2 4 4 2 2 10 5 6 3 8 7 11 9 12 7 10 11 8 7 9 7 2 J 1 1 "i 1 1 1.1 12 1 1 1 1 1 1 3 1 1.3 1 1.4 2 3 1.5 1 2 2 4 4 4 3 5 6 6 8 6 7 5 5 4 10 2 7 2 3 3 i 2 1.6 1 1 1 1 3 5 2 3 10 9 11 9 19 13 11 4 20 11 23 8 7 4 3 5 2 4 "i i 2 2 5 7 16 12 10 22 16 40 30 22 18 19 21 9 17 7 7 8 9 4 2 2 5 1 1 1.7. . "i i 4 2 2 4 1 2 1 s "2 4 1 1 1 1 1.8 1 2 4 1.9 1 2.0 ? 3 3 3 8 2 3 4 7 1 2 4 5 2 6 8 4 8 2 8 5 8 4 10 11 14 10 9 16 6 10 (3 8 2.1 "i i 1 "i "i 1 2.2 1 3 1 3 8 1 2.3 1 3 2 2 2.4 2.5 1 2 1 5 2 1 2 1 2 1 2.6 2.7. . 1 "i 2 1 ' 'i 2.8 2.9 1 2 4 8 1 1 1 3.O 3.1. . 1 3.2. . 1 1 3.3 1 3.4 3 i 3.5. . 2 1 3.6 3.7 2 2 1 2 1 1 1 "i 1 1 o 3 8 1 3 1 3.9. . 1 4.0 4.1 ---JT1 4.2 1 1 4.3 1 i 1 1 4.4 . .. 1 4.5 1 Total. . . . 3 15 27 78 144 194 320 337 306 410 310 226 156 105 35 21 10 8 2705 Percent weighing 2.5 pounds or less 46.8 Percent weighing over 2 . 5 pounds 53 . 2 The males constituted 52. 1 percent of the total number of pigs farrowed. 90 BULLETIN No. 226 [May, TABLE 13. RELATION OF WEIGHT OF PIGS TO SIZE; OF LITTER IN WHICH FARROWED: Females and Males Number of pigs per litter Females Males Total number studied Number Total weight, /6s. Average weight per pig. Ibs. Number Total weight, Ibs. Average weight per pig, Ibs. Number Total weight, Ibs. Average weight per Pig. Ibs. 1. . 2 13 30 80 125 177 238 327 309 400 278 234 121 94 24 11 8 12 4.9 39.0 84.8 216.6 346.5 463.5 615.1 853.7 748.4 974.9 676.3 569.6 283.1 215.2 58.4 26.1 20.2 29.0 2.45 3.00 2.83 2.71 2.77 2.62 2.58 2.61 2.42' 2.44 2.43 2.43 2.34 2.29 2.43 2.37 2.53 2.42 3 15 27 78 144 194 320 337 306 410 310 226 156 105 35 21 10 8 7.4 39.1 76.0 217.8 406.7 507.3 862.2 884.1 763.4 1070.4 773.5 559.2 384.6 264.3 89.8 50.7 22.6 21.5 2.47 2.61 2.81 2.79 2.82 2.61 2.69 2.62 2.49 2.61 2.50 2.47 2.47 2.52 2.57 2.41 2.26 2.69 5 28 57 158 269 371 558 664 615 810 588 460 277 199 59 32 18 20 12.3 78.1 160.8 434.4 753.2 970.8 1477.3 1737.8 1511.8 2045.3 1449.8 1128.8 667. 7 479.5 148.2 76.8 42.8 50.5 2.46 2.79 2.82 2.75 2.80 2.62 2.65 2.62 2.46 2.53 2.47 2.45 2.41 2.41 2.51 2.40 2.38 2.51 2 3 4 5 6 7 8 9 10 11 12 13 14. 15 16 18 20 Total or average. . . . Number in litters of 8 pigs or less. Number in litters of more than 8 pigs 2483 992 1491 6225.3 2624.1 3601.2 2.51 2.65 2.42 2705 1118 1587 7000.6 3000.6 4000.0 2.59 2.68 2.52 5188 2110 3078 13225.9 5624.7 7601.2 2.55 2.67 2.47 TABLE 14. RELATION OF AGE OF DAM TO BIRTH WEIGHT OF PIGS Age of dam, years Number of pigs Total weight of pigs, Ibs. Average weight per pig, /6s. 1. . 992 977 951 647 594 328 315 171 99 53 53 18 7 7 2415.7 2396.9 2429.0 1672.0 1541.2 868.3 813.6 462.4 281.2 150.5 143.4 54.0 15.9 25.0 2.44 2.45 2.55 2.58 2.59 2.65 2.58 2.70 2.84 2.84 2.71 3.00 2.27 3.57 1J. . 2 ... 2M 3. . 3^. .. 4 4M. . 5 ... 5% 6. . 6>$.. 7 ... 8 Total 5212 13269 . 1 2.55 Average weight of pigs from BO\ Average weight of pies from so vs 1 and 1J^ years old 2.44 2.61 ivs 2 years old or over. . . 1920] VARIATIONS IN FARROW 91 TABLE 15. RELATION OF AGE OP DAM TO NUMBER OF PIGS FARROWED DEAD OR IMMATURE Age of dam, years Number of pigs farrowed by sows of these ages Dead Immature Total number dead or immature Total number studied Percent dead or immature 1. 69 66 51 38 66 26 19 19 22 10 2 5 38 17 31 12 21 13 9 6 'i 3 107 83 82 50 87 3 28 25 22 10 3 8 1174 1058 1056 690 635 342 375 181 107 53 62 31 7 7 9.1 7.8 7.8 7.2 13.7 11.4 7.5 13.8 20.6 18.9 4.8 25.8 \y z 2 2K 3 .. 3J^ 4. . 4K 5 . : 5>^ 6 6>6 7 8 Total 393 151 544 5778 9.4 Percentage of pigs farrowed dead or immature from sows 1 to 2J^ ye Percentage of pies farrowed dead or immature from sows 3 years ok ars old 8.1 12.3 or over . . . TABLE 16. RELATION OF AGE OF DAM TO SEX OF PIGS Age of dam, years Number of pigs of each sex Number of pigs, sex of which was not obtained Total number studied Females Males 1.. . 547 497 487 331 298 162 143 88 48 19 37 11 1 4 580 544 530 347 327 167 195 89 59 34 24 17 6 3 47 17 39 12 10 13 25 4 'i 3 1174 1058 1056 690 635 342 375 181 107 53 62 31 7 7 \y z 2 2>^ 3 3H 4 4^ .... 5 5^ 6 6J^ 8 Total 2673 2922 171 5778 Percent . . 47.8 52.2 Percent from sows 1 and 1J^ years ol Percent from sows 2 years old and ov TABLE 17. TOTAL d Females Males 48.2 51.8 47.5 52.5 OF EACH BREED er NUMBER OF LITTERS Berkshire 363 37 78 4 67 Tamworth Large Yorl Crossbred ' Unknown 2 40 35 77 20 Chester White cshire Duroc-Jersey Total . . 720 bred. All litters in which the pigs were cross-bred, regardless of breeding of dams, are listed as cross- 2 All litters, in which the breeding is not definitely known, are listed as unknown. 92 BULLETIN No. 226 [May, a I 2 2 fe t, w 2 i PQ S.M CO'OINlOi'Si'JtD'* s !i O N N IN Cq (N N O +3 O ^ CO 00 1 >O U) * i-H t- w 1 |f saassaigs o N5COOINO M< TH (N CO t^ O IN 00 to .ojjtl a ft^: N OJ * O t- CO 00 Q ^lOt^OOTjfUSO s H,"o F-4 Q, t^OJOOt^WOJ-MOO 00 || 3 l-s.5 a n fe ^ IN TJ< rt CO M IN CO 00 to CO Number of litters lOOt^lNt-CO'fO IN t~ Sog (N i-l <-l >O CO IN > O 8* '5 a OJM 05 2222S2I22! 2 > a " ^^s, tl s. fflCOCOOW O 22S82 ~J3 1-IiS INWOOCO-HCOOOO-*-* >0 3 i gllpspss SpS , jx S*j IN OOfOOOtO o 00 ........*.. ll 3 TfoOC^l'-i-^OOOOCSiN H CO J2 E fi ?SS5f2SS2 1 5352532-33 3 Sjti 0) sli g g M 03 ^ WtfOO'-'OOCOOOCOO CO (N(NCS(N(N(NCer. Length of gestation period . . 114 9 114 4 114 7 Number of pigs per litter 7 21 8 72 7 96 Weight per litter 16 1 22 3 19.3 Weight per pig 2.26 2.51 2.41 53 Sows: Age at farrowing 1 yr. 2 yrs. Length of gestation period 114.7 114 114.4 Number of pigs per litter, 7 70 8 11 7 91 Weight per litter 18 8 22 2 20.4 Weight per pig 2 40 2.54 2.47 28 Sows: Age at farrowing 2 yrs Aver. Length of gestation period ; 114 8 114 7 114.8 6 71 7 93 7 32 Weight per litter . 16 3 21 2 18 6 Weight per pig 2.46 2.61 2.54 Sows WITH THREE LITTERS EACH 14 Sows: Age at farrowing 1 yr. /}/ yrs. % yrs. Length of gestation period 114.3 114 1 114 8 114 4 Number of pigs per litter 7.64 8.57 9.64 8 62 Weight per litter 16.7 22.3 23 20 5 Weight per pig 2 19 2 63 2 48 2 44 9 Sows: Age at farrowing 1 1 A yr. # yrs. 2% yrs. Length of gestation period 114.6 114.7 114.0 114 4 Number of pigs per litter 6 89 8 56 8 89 8 11 Weight per litter 16 4 21 8 23 6 20 4 Weight per pig 2.38 2.67 2.66 2 57 22 Sows: Age at farrowing 1 yr. % yrs. #l/ij yrs. Length of gestation period 114.9 114.0 114.7 114 5 Number of pigs per litter 8.05 10.27 9.05 9 12 Weight per litter 19 1 24 3 24 3 22 5 Weight per pig 2.37 2 50 2 64 2 51 11 Sows: Age at farrowing 2 yrs. 3 yrs. Length of gestation period 112.7 113 6 114 5 113 8 Number of pigs per litter 8.27 9.64 8.82 8 91 Weight per litter ... 20 3 24 7 23 7 23 Weight per pig 2.42 2.56 2.70 - 2.56 Sows WITH FOUR LITTERS EACH 7 Sows : Age at farrowing 1 yr. 1% yrs. 2 yrs. 2% yrs. Length of gestation period 113.5 114.0 114.8 114.8 114 3 Number of pigs per litter 7 86 10 29 10 57 10 43 9 79 Weight per litter 19.1 25.4 24.5 24 2 23 3 Weight per pig 2.43 2.54 2.45 2.32 2 42 5 Sows : Age at farrowing 1% yrs'. 2 yrs. #Jlj yrs. 3 yrs. Length of gestation period . ... 115 3 114 6 113 4 114 114 3 Number of pigs per litter 8 60 10.40 9 00 9 00 9 25 Weight per litter 19.8 25.6 24.8 22.4 22 9 Weight per pig 2.30 2.56 2.76 2.49 2.52 13 Sows: Age at farrowing 1 yr. # yrs. #K vrs. 3 yrs. Aver. Length of gestation period 114 6 113 8 114 5 114 4 114 3 Number of pigs per litter 7.46 10.00 9.31 10.62 9 35 Weight per litter 17.0 20.7 23.7 25.8 21.7 Weight per pig 2.31 2.36 2.46 2.67 2.51 Length of gestation period is given in days; weight in pound UNIVERSITY OF ILLINOIS-URBANA