Effects of choline supplementation on reproductive outcomes in ewe lambs and growth performace and carcass characteristics of their progeny

Traits associated with reproductive performance are among the most economically important. However, current estimates of average number of lambs born per ewe are only slightly better than compared to the 1970's. Furthermore, because of the seasonal nature of sheep production, 85% of lambs are born from January to May and this has negative downstream implications for carcass quality. Applied strategies to increase reproductive efficiency, particularly for young ewes, are critical. One potential strategy to improve reproductive performance is to manipulate the diet prio to and during pregnancy, which could have seconary benefits of programming resultant progeny to be more efficient. However, there is limited data, particularly in field settings, related to strategies that could be applied to breeding ewes that can also have subsequent impacts on the productive efficiency of their offspring. Choline is an essential nutrient and plays an important role in many cellular functions. Free choline can be found in plants and other feedstuffs but it is metabolized in the rumen.
Experiments in cattle and goats have demonstrated effects of choline on fertility and postnatal growth of offspring. We propose herein feeding rumen protected choline to ewes in optimal and suboptima mating seasons and evaluating its impact on subsequent reproductive outcomes as well as growth performance and carcass characteristics of the progeny.
The ojectives of the proposed research are:

1. To determine the effects of supplemental choline feeding around the time of mating on reproductive outcomes in ewe lambs during the fall and spring breeding seasons.

2. To assess the effect of supplemental choline during the time of mating on programming of postnatal growth efficiency of the resultant offspring.

3. To determine the effects of supplemental choline feeding around the time of mating on carcass yields and carcass characteristics for resultant offspring sent to slaughter. To determine the effects of supplemental choline feeding and season on reproductive efficiency of ewe lambs as well as the growth performance and carcass characteristics of the resultant offspring, a study will be conducted in the optimal (fall) and suboptimal (spring) breeding seasons at the USDA Meat Animal Research Center (see attached letter of support) in Clay Center, NE. In each season, 100 Polypay ewes (a combination of ewe lambs and mature ewes) will be randomly assigned to one of two treatment groups: control supplement or supplement containing rumen-protected choline (RPC).

Feeding of experimental supplements will be done using Smart Feeders and animals in the RPC treatment group will be fed to achieve an intake of 40 g/hd/d of RPC. Ewes will be fed the experimental supplements for approximately 3.5 weeks initiating at the start of the estrous synchronization protocol and ending approximately 10-12 days after mating.

For breeding, estrus will be synchronized using a standard protocol and ewes will be exposed to rams for a 4-day period. Rams will be fitted with marking harnesses and estrus and mating activity will be documented. During the experimental feeding period, periodic blood sampling will be performed to analyze serum levels of choline. Following mating, additional blood samples will be collected to determine serum progesterone levels as well as levels of markers associated with embryonic and placental function. Pregnancy will be assessed at 35 3 days and subsequently confirmed at 60 3 days of gestation via rectal ultrasonography. Prolificacy will also be determined at the 60-day pregnancy diagnosis.

At parturition, number of lambs born, number of lambs born alive, and lamb birth weight will be documented. Subsequent body weight measurements of the offspring will be recorded at 45 days and at weaning. A subset of wethers (n=60 per treatment) will be randomly selected for terminal slaughter/processing. In this subset, body weights will be recorded monthly form weaning to slaughter. At slaughter, samples will be collected from tissue/muscle for sensory evaluation, fiber typing, objective color and muscle chemistry. Carcass characteristics will be documented. Fat deposition patterns will be assessed at cross-sections of each primal cut. Carcass cutout and yield data will be collected during fabrication.

It is anticipated that supplementation of RPC will enhance reproductive efficiency and prolificacy in ewe lambs, particularly during the non-breeding season. Additionally, it is expected that, regardless of season, lambs born from mothers fed supplemental RPC during the mating period will have improved growth efficiency from birth to weaning and, for animals sent to slaughter, enhanced carcass yields and carcass characteristics.