Dietary effects on sow productivity to three parities - Year 2-3 of NPB #12-210 (NPB#13-259, Midterm)

Authors: Lents, Clay; STALDER, KENNETH - Iowa State University; SUPRAKORN, CHINA - Iowa State University; BOYD, DEAN - Hanor Family Of Companies; DEDECKER, ASHLEY - Smithfield Foods, Inc; Vallet, Jeff

Submitted to: National Pork Board Web Site <www.porkboard.org>
Publication Type: Research Technical Update
Publication Acceptance Date: 8/14/2018
Publication Date: N/A
Citation: N/A

Interpretive Summary: The long-term goal of this study is to discover how to optimally feed gilts during development in order to maximize their lifetime productivity. The first objective was to determine how feeding gilts diets that had standard levels of metabolizable energy (approximately 3,200 kcal/kg) but different levels of standard ileal digestible (SID) lysine during development affected growth rates, body composition, and pubertal development. Treatment diets were defined as high, medium, and low lysine with the content of SID lysine for high, medium, and low diets being 0.90%, 0.79%, and 0.68% (phase 1) and 0.68%, 0.60%, and 0.52% (phase2), respectively. The high lysine diet was developed to provide adequate levels of SID lysine. Diets were fed in two phases with phase 1 applied from 100 to 142 days of age, and a phase 2 fed until gilts were moved to the sow farm at 200 days of age. This study was conducted within a 75,000-sow commercial production system where pigs for the experiment were born over 42 consecutive weeks. Gilts were individually identified at birth were moved to the research gilt development unit (GDU) at 11 wk of age where they were assigned to treatment. Each treatment contained gilts from each litter. Boar exposure and detection of estrus began at 160 d of age using mature boars placed in pens with gilts daily. Blood samples for progesterone were collected from gilts that did not express pubertal estrus by 210 and 220 days of age in order to determine if they had ovulated. Gilts that did not display pubertal estrus by 220 days of age were injected with PG600 and observed for estrus. Estimates of body weight and measures of ultrasound backfat thickness and loin eye area were determined at 100, 140, 160, and 200 days of age, at puberty, and at first breeding. Gilts fed the medium and low lysine diet had progressively lower body weight gain, backfat thickness, loin depth and fat-free lean than gilts fed the high lysine treatment. Gilts fed the low lysine diet were proportionately fatter (fat:lean ratio) than gilts fed the medium or high lysine diets. Although dietary treatments did not affect the average age of puberty or the total number of gilts that reach puberty, a greater percentage of gilts fed the high lysine diet had a spontaneous pubertal estrus during the first 40 days of boar exposure. The majority of gilts that failed to reach puberty and had to be injected with PG600 were in-fact noncyclic, or prepubertal at PG600. Gilts that had a first estrus induced with PG600 were older and heavier than gilts that had a spontaneous first estrus, but they also had less backfat and loin depth, suggesting they were less physiologically mature. Overall, gilts fed the high lysine diet had greater size, weight, and mass of metabolic tissue than gilts fed the other diets and these differences persisted through first breeding. Gilts had less backfat at first breeding compared with first estrus, which probably reflects management of gilts in breeding stalls. However, pregnancy and farrowing rates were quite high. These results indicate that growth rate and body composition of gilts can be slowed and altered without negatively affected age at puberty or the total number of pigs that reach a first estrus spontaneously. Improving the number of gilts that have a pubertal estrus earlier and reducing the number of gilts that need PG600 to become pubertal are areas of opportunity on which to focus to improve gilt development.

Technical Abstract: The main objective was to determine how dietary manipulation of growth and body composition of gilts affects pubertal development. Diets had similar levels of metabolizable energy (ME: approximately 3,200 kcal/kg) but different levels of standard ileal digestible (SID) lysine. Diets were defined as high, medium, and low and concentrations of SID lysine were 0.90, 0.79, and 0.68% for phase 1, and 0.68, 0.60, and 0.52% for phase 2, respectively. Maternal line gilts (Large White x Landrace crossbred) were born over 42 consecutive farrowing weeks in two farms in a 75,000-sow commercial production system. Gilts (n = 3,024) entered the research gilt development unit (GDU) at 11 wk of age where they were blocked by litter of origin and allocated to pens. Gilts were enrolled on study (n = 1,008 per treatment) at 100 days of age when feeding of the Phase 1 diet began. Phase 1 continued for 6 weeks followed by phase 2 until 200 days of age when gilts were moved to sow farms. Gilts were exposed to mature boars in their home pen daily to stimulate pubertal estrus beginning at 160 days of age. At 210 and 220 days of age, blood samples were collected from all gilts that failed to reach puberty (indicated by standing estrus) and analyzed for serum concentrations of progesterone indicating luteal function (= 1 ng/mL). After 220 days of age, gilts were eligible to receive PG600 to induce a pubertal estrus. Gilts were eligible for breeding at their second or third estrus if they were estimated to weigh approximately 135 kg. Measures of body size (caliper and flank to flank), body weight, and ultrasound measures of backfat and loin depth were collected at 100, 142, 160 and 200 days of age, as well as at first estrus and first breeding. Growth rates, loin depth, and backfat were progressively reduced (P < 0.05) as the concentration of SID lysine in the diet decreased. Gilts fed the low lysine diet, however, were proportionally fatter (P < 0.05), as indicated by fat:lean ratio, than gilts fed the other treatments. These differences largely persisted through first estrus and breeding with the exception of the fat:lean ratio. A greater percentage of gilts that were fed the high lysine diet exhibited estrus during the first 40 days of boar exposure (17.9%) than did gilts fed the medium and low lysine diets (11.4 and 9.1%, respectively; P < 0.0001). There was no difference between treatments in the percentage of gilts to express a spontaneous first estrus, which was 54.5, 56.3, and 53.8% for high, medium, and low, respectively. Gilts that had a spontaneous first estrus were younger and lighter, but had more backfat, lion depth, and a greater lifetime growth rate than gilts that required PG600 to induce first estrus. Despite the fact that gilts fed the high lysine treatment during development were bigger, weighed more and had more metabolic tissue at first breeding than gilts fed the other treatments, there were no differences between treatments for conception or farrowing rates. There were no differences between treatments in the number of gilts removed from the study or for removal reasons. Mortality was the primary reason for loss of gilts in the research GDU (47%) with unexpected death accounting for 30.6% and euthanasia accounting for 16.4% of all removals during this time followed by injury to tails (19.2%) and poor body condition (18.3%). When considering only gilts that entered the sow farm at 200 days of age, 27% failed to produce a first litter. It is estimated that approximately 39% of gilts that entered the sow farm will produce a third litter. It is concluded that lysine content of the diet can be reduced to limit growth and alter composition of gilts during development and that these differences will be maintained through first breeding. Dietary-induced differences in growth and body composition do not negatively affect overa