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The objective was to determine degree of feed restriction during development required to optimize reproductive performance and efficiency in gilts. Different patterns of growth and reproductive performance through d 30 of gestation were investigated. At 13 wk of age, 41 kg BW, 192 white crossbred gilts were penned individually and assigned to receive 7/8, 3/4, 5/8 or 1/2 of ad libitum energy intake. At 25 wk of age, gilts were moved to group pens, fed ad libitum, and an 11-wk estrous detection period initiated. Gilts were inseminated at first detected estrus (puberty). Gilts were slaughtered at 30 d of gestation. Feed restriction during development resulted in differences in BW and backfat thickness at start of the breeding period and differences in daily feed intake (ADFI) during breeding. The lightest, leanest group at the start of breeding consumed the most feed during breeding and had the fewest no. of days to puberty, followed by the heaviest, fattest group that consumed the least feed during breeding. Treatments did not differ in ovulation rate or live embryo numbers (P > 0.39). Significant relationships between quantity of GE consumed during development and many development and reproductive performance variables were evident, e.g., BW and fatness at start of breeding, puberty, pregnancy, and ovulation rate. Ad libitum intake during breeding negated many effects of feed restriction during the development period. In contemporary swine production, use of managed nutritional strategies that include periods of restriction, and periods of ad libitum access to feed, may allow improvements in efficiency of pork production. 25 wk Breeding Lv Treat- BW, ADFI, Days to % Embryo ment kg kg (a) puberty pubertal /gilt (a) 1/2 Adlib 77.8 3.76 15.3 85.4 8.9 5/8 Adlib 92.8 3.28 24.5 79.1 8.4 3/4 Adlib 103.7 3.19 27.9 87.5 8.6 7/8 Adlib 112.7 3.06 22.4 85.4 7.8 Pooled SE 0.5 0.05 1.3 -- 0.4 Lv Treat- Embryo ment efficiency (a b) 1/2 Adlib 0.0407 5/8 Adlib 0.0298 3/4 Adlib 0.0273 7/8 Adlib 0.0230 Pooled SE 0.0014 (a) All gilts assigned (b) Live embryos per kg feed 13 to 30 d gestation Key Words: Gilts, Puberty, Growth

Development of gilts that conceive early and continue to produce offspring is a primary objective of swine production. The objective of this study was to determine the degree of feed restriction during development required to optimize reproductive performance and efficiency in gilts. The effects that various patterns of growth had on reproductive development and performance of gilts through d 30 of gestation were investigated. At 13 wk of age and 41 kg BW, 192 white crossbred gilts were penned individually and assigned to receive 87.5%, 75%, 62.5%, and 50% of predicted ad libitum energy intake. The study was replicated in two seasons. At 25 wk of age, gilts were moved to group pens and allowed ad libitum access to feed, and estrous detection was initiated. Gilts were inseminated at first observed estrus and those recycling were remated. Post-mating gilts were fed 1.5x maintenance in stalls. Gilts that did not return to estrus 17 to 30 d after mating were slaughtered at 30 d of gestation. Reproductive tracts were collected and numbers of corpora lutea and live embryos were recorded. Feed restriction during development resulted in differences in BW and backfat thickness at the start of the breeding period and differences in feed intake during breeding. Gilts subjected to the greatest feed restriction during development consumed the greatest quantity of feed during breeding. Feed intake during breeding was associated with BW and backfat gain during breeding. The treatment group that entered breeding lightest and leanest (50% of predicted ad libitum intake) had the least number of days to first estrus, followed by the fattest, heaviest group (87.5% of predicted ad libitum intake). Treatment groups did not differ (P > 0.38) in ovulation rate or live embryo numbers. Significant relationships between quantity of GE consumed during development and variables considered important in reproductive development and performance were evident, such as BW and fatness at start of breeding and first detected estrus, and ovulation rate. Variation in dietary energy during the development period impacted many aspects of reproductive development and performance. However, coupling restricted energy intake during development with ad libitum intake during breeding negated many of the effects of feed restriction during the development period. Key Words: Gilts, Growth, Pregnancy, Puberty

Deals with a study which investigated patterns of growth on reproductive development and performance of gilts through the first farrowing. Breed of gilts used in the study; Results and discussion; Implications of the study.

Discusses the abstract of the study 'Efficacy of restricted/ad libitum feeding strategy for group-fed gilts during development,' presented at the American Society of Animal Science's Midwestern Branch conference on March 17-19, 2003, in Des Moines, Iowa.

Discusses the abstract of the study 'Effects of an intraperitoneal bolus injection of L-phenylalanine on physiological paramaters in weanling pigs,' presented at the American Society of Animal Science's Midwestern Branch conference on March 17-19, 2003, in Des Moines, Iowa.

Discusses the abstract of the study 'Effects of sire line, sire and sex on plasma urea nitrogen, body weight and backfat thickness in offspring of Duroc and Landrace boars and heritabilities,' presented at the American Society of Animal Science's Midwestern Branch conference on March 17-19, 2003, in Des Moines, Iowa.