Some Feeding and Management Factors Affecting Age at Puberty and Related Phenomena in Chester White and Poland China Gilts

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Abstract
An experiment of factorial design was used to study the effects of three variations of feeding and management upon various reproductive phenomena in 48 Chester White and 48 Poland China gilts. The average age at puberty of gilts in this study was 201 days with a standard deviation of 13.2 days, while the average weight at puberty was 195 pounds with a standard deviation of 35 pounds. Age at puberty was less variable than weight at puberty, the coefficients of variation being 6.6% and 18.0%, respectively. Gilts which were born later in the spring farrowing season tended to reach puberty at a younger age. There was significantly greater variability in length of the first estrual cycle in the Chester White than in the Poland China gilts. Full-fed gilts tended to reach puberty earlier than limited-fed gilts, and gilts which received the low protein ration were 6 days younger at first heat than those which received the high protein ration (P≤0.05). There was not an over-all significant difference in age at puberty between the two breeds, but the Chester Whites were 11 days older than the Poland Chinas in the pasture lots (P≦0.01) and 1 day younger in the dry lots. Poland China gilts were 9 days younger at puberty on pasture than in dry lot (P≦0.05) while the Chester White gilts were 3 days older on pasture than in dry lot. Full-fed gilts of each breed were significantly heavier at puberty than limited-fed gilts. Full-fed Chester White gilts were heavier than full-fed Poland Chinas (P≦0.01). High protein fed gilts were 5 pounds heavier at puberty than low protein fed gilts on pasture, but were 24 pounds lighter in dry lot. The average ovulation rate at first heat over all lots was 9.8 eggs per gilt. Full-fed Chester White gilts ovulated 2.9 more eggs at first heat than did limited-fed Chester Whites (P≦0.01), whereas full-fed Poland China gilts exceeded the limited-fed Poland Chinas by only 0.7 egg. High-protein fed gilts tended to ovulate more eggs than low-protein fed gilts if on pasture, but fewer eggs if in dry-lot (P≅0.07). At the second heat period, the average ovulation rate was 11.8 eggs per gilt, an average increase of two eggs per gilt over the ovulation rate at first heat (P≦0.01). Full-fed gilts ovulated 1.1 eggs more per gilt than did limited-fed gilts, a difference which was significant over all lots. Also, Chester White gilts ovulated an average of 3.4 eggs per gilt more than Poland China gilts, a difference which was highly significant over all lots. Here again, the high-protein gilts ovulated more eggs than low-protein gilts on pasture but fewer eggs in dry-lots, and in this instance the interaction was significant. The over-all unweighted mean fertility of ova in this study was 93%. There were no significant differences in fertilization rate between the breed-treatment groups. Nor was there any difference in fertility due to the breed of boar to which the gilts were mated. The average number of normal embryos per gilt at 25 days was 6.7. These embryos represented approximately 55% of the ova ovulated at second heat. Of the remaining 45%, approximately 7% were accounted for by an observed failure of fertilization, leaving 38% which were lost presumably due to embryonic death. Limited-fed gilts tended to have more embryos at 25 days of gestation than the full-fed gilts. When compared on a percentage basis the difference was statistically significant over all lots, the limited-fed gilts having 67% of the corpora lutea of second heat represented by normal embryos while the full-fed animals had only 43% embryos. However, limited feeding of the low-protein ration to Poland China gilts in dry-lot resulted in a reduction of both number and size of embryos present at 25 days. The over-all average size of embryos at the 25th day of pregnancy was 16.9 mm, with the embryos from the Chester White gilts averaging 17.6 mm as compared to 16.2 mm for those from the Poland China gilts (P≦0.01). Copyright © . .

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