Location: Reproduction ResearchTitle: Optimal dietary protein for the development of gilts – NPB #15-119 (14-235-Year2) Author
Submitted to: National Pork Board Web Site <www.porkboard.org>
Publication Type: Research Technical Update
Publication Acceptance Date: 8/26/2015
Publication Date: 9/16/2015
Citation: Vallet, J.L., Calderon-Diaz, J., Stalder, K., Boyd, D., DeDecker, A., Lents, C. 2015. Optimal dietary protein for the development of gilts – NPB #15-119 (14-235-Year2). National Pork Board. Available: http://research.pork.org/FileLibrary/ResearchDocuments/15-119-Vallet-USDA%20(14-235-Yr2).pdf. Interpretive Summary: This experiment was undertaken to develop diets that could be fed ad libitum to developing gilts that would result in differences in growth rate or body composition during development. A further component of the experiment was to determine whether diets affected age at puberty. This study is a prelude to a larger study to measure dietary affects on sow productivity to third parity. Diets were developed that had normal levels of metabolizable energy (~3200 kcal/kg) but differed in SID lysine levels, with a control designed to be adequate, and two further diets with progressively less SID lysine (medium and low lysine, respectively). Diets were fed in two phases, a grower phase that was applied for 6 weeks, and a finisher phase that was fed from then until gilts left the experiment at 220 days of age. Diets were begun at 100 days of age. Gilts were weighed and measured for backfat and loin depth by ultrasound when diets began and at 28 day intervals until 212 days of age. Blood samples were collected from gilts that had not expressed estrus by 210 and 220 days of age for progesterone analysis to assess whether they were prepubertal or behaviorally anestrus. Finally, at 220 days of age all gilts not experiencing a standing estrus were injected with PG600 and observed for 1 week to determine their estrus response. Gilts on this trial experienced a porcine epidemic diarrhea virus outbreak at approximately the time estrus detection and boar exposure was begun. It is likely that this outbreak temporarily impaired the growth of gilts, but there was no uninfected control to allow conclusions to be drawn on the PED effects, if any. On the other hand, all treatments were similarly afflicted, thus conclusions from the trial regarding comparisons among diets are likely to be valid. Compared to the Control diet, the medium and low SID lysine diets progressively reduced body weight, loin depth and backfat gain in gilts, with no changes in relationships (body composition) between loin depth and backfat. Only approximately 30% of gilts reached puberty by 220 days in this experiment, likely due to the effects of PED. The number of gilts experiencing puberty per the number of gilts exposed to the boar was numerically less for the medium and low lysine diets, but these differences were not statistically significant. However, mean age at puberty was significantly greater in gilts fed the low lysine diet. Most noncyclic gilts experienced puberty in response to PG600, suggesting that they were prepubertal, rather than behaviorally anestrus. However, about half the gilts that were confirmed to be behaviorally anestrus using progesterone concentrations responded to PG600 by exhibiting standing estrus within one week. These results indicate that we were successful in developing ad libitum fed diets that resulted in reduced growth of developing gilts by reducing the lysine level of the diet. Although the number gilts reaching puberty did not differ, age at puberty in the low lysine diet was 7 days older than the control and medium lysine diets. These diets can now be used to determine effects of reduced growth rates on retention of gilts in the breeding herd.
Technical Abstract: A previous trial funded by the National Pork Board indicated that within the practical range of commercially available ingredients for swine diets, metabolizable energy (ME) content in the diet could not be used to alter the growth rate of developing gilts, and had only minor effects on fat deposition. In addition, a 15% reduction of SID lysine levels commonly used in industry diets to develop gilts failed to reduce growth rates. In the current trial, diets were developed that had similar ME levels (3135-3278 Mcal/kg), and different SID lysine levels of 0.90, 0.79 and 0.68% (grower diets) and 0.68, 0.60 and 0.52% (finisher diets) for control, medium and low lysine levels. Grower diets were fed beginning at 100 days of age and continued for 6 weeks, followed by finisher diets until 220 days of age. At commencement of diets and at 28 day intervals until the end of the trial, gilts were weighed and measured for back fat and loin depth using ultrasound. Gilts were exposed to mature boars beginning at 160 days of age and observed for estrous behavior once a day. At 210 and 220 days of age, blood samples were collected from all gilts that failed to reach puberty, as indicated by standing estrus. At 220 days of age, gilts received an injection of PG600 to stimulate the onset of puberty, and gilts were observed for estrous behavior for an additional week. Results indicated that growth of body weight, loin depth and back fat were progressively reduced as SID lysine in the diets were reduced, indicating that diets reduced growth rate but did not alter body composition. Age at puberty was significantly greater in gilts on the low lysine diets compared to control and medium lysine diets (209±2 days versus 202±2 and 198±2 days, respectively). The percentage of gilts reaching puberty before 220 days of age was low but did not differ among treatments (38, 31 and 28% for control, medium and low lysine, respectively). A majority of gilts that had not reached puberty experienced puberty in response to PG600 injection, and this percentage did not differ between diets (85%, 76% and 79% for control, medium and low lysine diets, respectively). The gilts in this experiment experienced a porcine epidemic diarrhea virus outbreak in unison, but varied in age at the time of the outbreak (93 to 160 days of age) because they entered the trial on a weekly basis over a 9 week period. This may explain the low rate of puberty attainment. In conclusion, these results indicate that holding ME constant and decreasing SID lysine in diets was able to delay growth of gilts without altering body composition. The reduced growth rate increased age at puberty in the low lysine diet, but did not alter the percentage of gilts reaching puberty by 220 days of age. These diets will be useful in determining the effects of reduced growth rate in ad libitum fed gilts on sow productivity in the breeding herd.