ON COMMERCIAL poultry farms during

Effect of Date of Hatch on Weight F. P. JEFFREY Department of Poultry Husbandry, Rutgers University, New Brunswick, New Jersey (Presented at annual meeting June, 1940; received for publication May 23, 1940) ON COMMERCIAL poultry farms during recent years there has been an increase in the production of laying pullets hatched out of the normal season. General observations on New Jersey farms have indicated that fall-hatched pullets tend to produce more small eggs than do springhatched pullets. Various explanations have been suggested, including the claim that fall-hatched pullets are deficient in body, or that in particular instances the inherited ability to produce large eggs was lacking. In view of the fact that Bennion and Warren (1933) have shown that high temperatures tend to reduce egg, it is more logical to assume that fall-hatched pullets produce more small eggs than do spring-hatched pullets because of the difference in temperature prevailing in New Jersey during the first few months of egg production of the spring and fall-hatched pullets. The above assumption explains satisfactorily why Card (1922) observed that.2 percent of the total year's egg production of November-hatched pullets averaged grams or less each, while the June-hatched pullets produced only 1.7 percent of their eggs in this egg group. The data of Upp (1927) also agree to a marked degree in that birds having a mean date of sexual maturity of November 2 showed a mean annual egg of 50. grams, while birds having a mean date of sexual maturity of April 18 showed a mean annual egg of 46.96 grams. 1 Journal series paper of the New Jersey Agricultural Experiment Station, Department of Poultry Husbandry. [7] MATERIALS AND METHODS Five pens of Single Comb White Leghorns hatched on June 17, 19; September 1, 19; November 1, 19; January IS, 1938; and April 1, 1938, were used. Pedigreed chicks were supplied by eight breeding pens except for the November and January hatches, when it was necessary to use some chicks from pen matings. The pen matings consisted of birds of the same strain, and, since the pedigree matings were not selected for either number or of egg, it is felt that the five different hatches of pullets were essentially the same in respect to their inherited ability to produce large eggs. All hatches were fed and managed as much alike as was possible. Except for the addition of an extra S percent alfalfa leaf meal to the mash for the first four weeks, chicks and laying birds received the same mash; namely, the laying mash recommended by the New Jersey Experiment Station. From 6 to 24 weeks of age the chicks had free choice of mash and grain, and in the laying house the birds had free choice of mash, cracked corn, and whole oats. During the growing period the birds were allowed free range. From 24 to 76 weeks of age the laying birds received 15 hours of light each day. The number of pullets at the start of the laying year was as follows: June hatch, 91; September hatch, ; November hatch, 93; January hatch, 94; and April hatch, 100. Each hatch was housed and maintained as a separate unit. The laying year was divided into 13 fourweek periods (24-76 weeks, inclusive). All

8 F. P. JEFFREY eggs were weighed individually at the time of trapnesting on a scale with a range of 18 to 30 ounces per dozen. In calculating mean annual egg, any egg weighing less than 18 or more than 30 ounces to the dozen was listed as weighing 18 and 30 ounces to the dozen, respectively. The number of eggs weighed from each of the hatches was as follows: June, 12,275; September, 7,781; November, 12,741; January, 10,696; and April, 12,191. At the end of each 28-day period at least SO percent, and in most instances over 80 percent, of the birds in lay were weighed individually. The mean body of the birds in lay was calculated for each 28-day period by taking an average of the s at the beginning and at the end of the period. readings in the laying house were taken twice daily, at 7:00 a.m. and 5:00 p.m., and the mean daily temperature calculated by averaging the two readings. production was calculated on a hen-day basis and no culling was practiced at any time. RESULTS Relation of egg to age of bird. The rate of increase in egg throughout the laying year varied widely in the different hatches. A large part of this variation in rate of increase was caused by the wholly different temperature environments prevailing in relation to age of bird. It can be seen in Table 1 that the September and November hatches showed a consistent period to period increase in egg throughout the first laying year. In a few instances the egg remained stationary for two succeeding periods, but in no period was there a decrease as the year progressed. This can be explained on the basis that high temperatures prevailed during the first half of their laying year, or during the part of the laying year when it was normal for birds to increase their egg at a rapid rate. The June hatch increased its egg each period with two exceptions, namely, at -56 and -76 weeks when slight decreases occurred. The decrease at -56 weeks can be accounted for by the fact that there was an increase of 6 F. over the - week period. The decrease at -76 weeks cannot be explained on the basis of temperature change. The January hatch showed a steady increase in its egg up to the 60-64 week period (early April) and then showed a decrease each succeeding period as the temperature continued to increase. The April hatch increased its egg up to the -56 week period (April). As the temperature rose during the summer months, egg decreased, remained stationary for three periods, and then finally responded to a drop in temperature during early September (-76 weeks) by increasing again. Warren (19) in a study of egg size in 11 localities in latitudes extending from the equator to Scotland concluded that temperature was an important factor in determining the shape of the annual egg curve. size was observed to increase throughout the year when the maximum temperature seldom exceeded F. The data presented in this paper supplement the above statement in that it was observed that egg increased throughout the year even when the mean temperature exceeded F. for a period of three months, provided that the high temperature occurred during the early part of the laying year, or during the period when it was normal for egg size to increase most rapidly. Relation of egg to temperature. Figure 1 illustrates the pronounced effect of temperature on the egg of two flocks of the same breeding but hatched at widely separated periods; namely, June

EFFECT OF DATE OF HATCH ON EGG WEIGHT 9 and November. For the first five periods the June hatch laid the heavier egg because of the low temperature which prevailed, and in spite of the fact that the TABLE 1. Relation of egg to age, temperature, body, and egg production egg 20.6 21.0 19.5 19.8 19.3 22.7 22.3 21.3 22.1 22.5 23. 23 22 24, 24. 24.0 23.6 25.1 23.9 25.2 26.3 24.7 26.1 25.8 25.2 26.5 26.5 24.8 24-28 weeks of age temperature degrees F. 78 60 body grams 1382 14 1590 10 1464 production percent 29 14 18 egg 21.4 21.6 20.7 20.6 21.3 28-32 weeks of age temperature degrees F. 80 body grams 10 14 1609 19 15 32-36 weeks of age 36-40 weeks of age 17 17 19 16 15 40^14 weeks of age 74 78 1591 16 18 17 12 64 56 45 53 23.1 23.0 22.1 23.2 23.6 23.3 24.7 80 1536 1645 18 11 1597 - weeks of age 79 41 13 16 16 12 13 - weeks of age -56 weeks of age 77 40 16 1646 1730 17 16 50 38 24.8 26.2 25.0 76 1606 1688 11 1804 17 56-60 weeks of age 60-64 weeks of age 79 40 15 1716 1714 1750 17 46 49 24.3 26.0 75 77 1497 13 17 1769 10 64-68 weeks of age 68- weeks of age 41 78 12 1699 17 1798 1711 30 32 23 26.2 26.1 25.1 71 80 11 1691 18 1805 10-76 weeks of age 24-76 weeks (average) 77 16 1698 1898 1833 1745 24 16 23.3 23.2 24.0 15 16 14 17 18

10 F. P. JEFFREY -* November hatch -*June hatch 24-88 28-32 32-36 36-40 40- - 46- -56 56-60 60-64 64-68 68- -76 Age in weeks body of the November hatch for this period averaged 1,9 grams while that of the June hatch averaged 1,5 grams. The flocks changed position in respect to their mean egg at the sixth period (- weeks), or at the point when the mean temperature for each flock was almost identical. For the last seven periods of the laying year the November hatch laid the heavier egg, because during this period a lower temperature prevailed for them than for the June hatch. Another variable which might be considered in relation to the data presented in Figure 1 is age at first egg. The mean age at first egg (days) for the different hatches was as follows: June, 186; September, 193; November, 1; January, 188; and April, 181. Since it is known that early sexual maturity is associated with small size of egg at the beginning of lay, FIG. 1. Relation of egg to temperature. it is possible that some of the difference in the of eggs produced by the June and November hatches is the result of the 20-day difference in age at sexual maturity. It is hardly conceivable, however, that this difference in egg, if caused by a difference in age at first egg, alone would persist for a period of almost five months. Rate of egg production does not appear to be a factor in the expression of egg as illustrated in Figure 1. For the first five laying periods the June hatch laid at the rate of percent and the November hatch at the rate of percent. For the last seven periods the November hatch averaged 41 percent and the June hatch 36 percent in rate of egg production. In other words, in this particular example, larger egg size was associated with higher egg production. Table 2 shows that a high temperature

EFFECT OF DATE OF HATCH ON EGG WEIGHT 11 during the first few months of lay was associated with the production of a relatively high proportion of pullet and peewee eggs. It should be noted that the November hatch produced 22 percent and the January hatch produced IS percent pullet and peewee eggs, while the June hatch produced only 8 percent of such eggs. The mean annual egg of the November hatch was lower than that of the January hatch because a high temperature prevailed for Date of hatch June September November April TABLE 2 Relation of egg to date of hatch of the laying year for the April hatch, which allowed the expression of a high percentage of large eggs, and high temperature prevailed at the end of the laying year, or at the time when it reduced egg size and still allowed the production of eggs weighing more than 24 ounces to the dozen. Thus, the proportion of large, medium, pullet, and peewee eggs produced by different flocks of the same breeding would appear to be determined largely by Percentage of total year's egg production which was Large (24 and over) 46 I Medium (21-23 oz.) per ) 32 27 27 the first five months of lay for the former, while the latter had only two-and-one-half months of high temperature at the beginning of the laying year. This difference in temperature environment during the early part of the laying year was important because the rate of increase in egg is normally greater during this period, and because more eggs are produced by a flock during the early part of the laying year than during the latter part. The June and September hatches produced a low percentage of pullet and peewee eggs and a high percentage of medium eggs. This condition is to be expected, since in each instance egg production began during the cold months, which would tend to result in the production of a heavier egg. Then, previous to, and in the middle of, the laying year high temperature prevailed, which had the effect of reducing egg size to the extent that a high proportion of medium eggs was produced. Low temperature prevailed in the middle Pullet (19-20 oz. per ) 7 8 IS 10 7 Peewee (18 and under) 1 1 7 S 3 Average annual egg 23.32 2 23.15 4 23.95 the interaction of age of bird and prevailing temperature. As Warren (19) has pointed out, it is difficult to state the minimum temperature which affects egg size when working with pullet year egg size curves. Because of the inherent tendency for egg size to increase throughout the pullet year, it is impossible to determine the minimum point at which temperature affects egg size from the data presented in this paper. Since the periods of low and high temperature occur at different age levels with each of the five hatches, it is difficult to evaluate the effect of compensation which logically would follow each period of high or low temperature. Relation of egg to body. The data selected for illustration in Figure 1 show that for a period of about five months the June-hatched birds laid heavier eggs than the November-hatched birds, even though the latter were considerably heavier in body. This observation

12 F. P. JEFFREY Age in weeks 24-28 28-32 32-36 36^0 40- - - -56 56-60 60-64 64-68 68- -76 TABLE 3. Relation between egg and body Above mean for period 20.1 21.0 21.9 22.8 24.2 24.3 25.0 25.7 25.6 25.6 Body 69 45 Below mean for period 20.0 21.4 22.6 23.3 23.9 24.2 24.1 24.3 25.3 49 49 71 75 60 53 has significance in that it indicates that flock body is tertiary to prevailing temperature and age of bird in its importance in determining egg. Other examples which show that flocks of light body sometimes produce larger eggs than do flocks of heavy body, when age and breeding are constant factors, are to be found in Table 1. In a comparison of the April and September hatches, it is found that the April hatch produced larger eggs from the age of 36 to 56 weeks, and during this period the September-hatched birds were heavier in body. Then from 56 to 76 weeks of age the September hatch produced the larger eggs and was slightly lighter in body. Likewise, from 64 to 76 weeks of age the January hatch produced smaller eggs than the September hatch, but was decidedly heavier in body. On the other hand, there are many examples in the data of Table 1 to show the opposite condition; namely, that large body size and large egg size are closely correlated, and it is certainly true that both egg size and body size increased in all hatches during the first laying year. It is equally true, however, that the rates of increase in egg size and body size were by no means identical, and it appears that the role of temperature in determining the rate of increase in egg size is greater than that of body. In Table 3 it is shown that during 3 of the 13 periods (28-32, 32-36, and 36-40 weeks of age) large egg size is associated with small body size, and during each of these periods the large egg size was accompanied by low temperature. Of the remaining 10 periods, large body size was associated with large egg size, and in all but three periods (24-28, 64-68, and -76 weeks of age) the large egg size was accompanied by the lower temperature. Relation of egg to rate of egg production. The data in Table 4 show that the relation between egg and rate of egg production is superficial when age of bird and temperature are considered. Rate of egg production in this table has been calculated on a hen-day basis where all birds laying less than 3 eggs in any 28-day period are omitted. By eliminating the Age in weeks 24-28 28-32 32-36 36-40 40- - - -56 56-60 60-64 64-68 68- -76 TABLE 4. Relation of egg to rale of egg production Percent egg producton Above mean for period 19.7 21.1 22.4 23.1 23.1 25.2 25.3 59 74 76 Below mean for period 20.3 21.2 21.9 22.9 24.0 25.0 24.7 25.7 25.6 46. 56 50

EFFECT OF DATE OF HATCH ON EGG WEIGHT 13 non-laying birds the percentage egg production is a good index of rate of lay. During 3 of the 13 periods (32-36, 36-40, and 56-60 weeks of age) egg production above the mean for the period was accompanied by a larger egg size than egg production below the mean for the period. In all of these instances the higher rate of production was accompanied by a lower mean temperature than was the lower rate of egg production. During the other 10 periods high egg production was associated with small egg size, but, except for one instance (28-32 weeks of age), the small egg size was associated with a higher temperature. DISCUSSION In studying the effect of date of hatch on egg the problem resolves itself into an evaluation of the effect of age, temperature, body size, and rate of egg production on egg. The data have shown that temperature has a very important role in the expression of egg. It is certainly true that prevailing temperature must be considered when determining the phenotype of a bird in studies on the inheritance of egg. This study would tend to invalidate the use of rate of increase in egg (the number of days required to reach an arbitrary egg standard) as a measure of a bird's egg size phenotype. Not only does date of hatch influence the proportion of different, large, medium, pullet and peewee eggs, but it also affects mean annual egg. Since there is sucha wide variety of climates in the United States it is likely that mean annual egg of birds of the same breeding and the same date of hatch would not be the same in southern and northern sections of the country. SUMMARY November- and January-hatched pullets produced more pullet and peewee eggs than did birds hatched in April, June, and September. June- and September-hatched pullets produced a high percentage of medium eggs, while January- and April-hatched pullets produced a high percentage of large eggs. of birds of the same breeding appeared to be determined at any particular time by the interaction of age, temperature, and body size. Rate of egg production was not of great importance in relation to egg. Because of the association existing between age of bird and body size, the effect of temperature was expressed chiefly in changing the rate of increase in egg of the different hatches. After body maturity was reached, high temperature tended to reduce egg size. In some instances small birds produced larger eggs than did large birds of the same age and breeding when below normal temperature prevailed for the former and above normal for the latter.. REFERENCES Bennion, N. L., and D. C. Warren, 1933. and its effect on egg size in the domestic fowl. Poul. Sci. 12:69-82. Card, L. E., 1922. The influence of season of hatching on egg production and related characters of White Leghorns. Thesis for degree of Doctor of Philosophy, Cornell University. Upp, C. W., and R. B. Thompson, 1927. Influence of time of hatch on hatchability of the eggs, rate of growth of the chicks, and characteristics of the adult females. Oklahoma Agr. Exp. Sta. Bui. 1 :3-36. Warren, D. C, 19. Effect of temperature on size of eggs from pullets in different latitudes. Jour. Agr. Res. 59:1-4.