Date of Graduation

2018

Document Type

Thesis

Degree Type

MS

College

Davis College of Agriculture, Natural Resources and Design

Department

Animal and Nutritional Sciences

Committee Chair

Marlon Knights

Committee Co-Chair

Eugene Felton

Committee Member

Kevin Shaffer

Abstract

Ewe lambs comprise 30% of the breeding flock; however, fertility is 20-30% lower than that of an adult ewe. Lower fertility has been correlated with lower ADG, liveweight, and body composition prior to breeding and research suggests that it can be improved with proper nutritional management. The objective of this research was to evaluate the effects of pre-breeding management practices on ewe lamb fertility.;In replicate 1, 313 Dorset X Texel (DT) and 74 Katahdin (KT) ewe lambs were assigned to a high (0.68 kg/head/day) or low (0.23 kg/head/day) grain supplementation for two months prior to breeding. Liveweights were recorded bi-weekly to calculate ADG and lifetime weight day averages (LWDA) and blood serum was collected by-weekly to determine estrous cyclicity. Half of each treatment group received progesterone pre-treatment prior to ram introduction. Estrous response was observed 96 hours and pregnancy diagnosis was performed 30 days and 60 days after synchronization. Replicate 2 consisted of 68 DT ewe lambs supplemented high (0.91 kg/head/day) or low (0.45 kg/head/day) grain supplementation for four weeks prior to synchronization. All other aspects of the experimental design remained the same as replicate 1. Data from DT ewe lambs in replicates 1 and 2 were pooled for statistical analysis to determine the main effects of nutritional treatment, progesterone pretreatment, breeding weight category, average daily gain category, weight day average category, and each respective interaction. In all replicates, an ANCOVA with breeding age as the covariate was utilized to determine the main effects and interactions, as well as if ADG, breeding weight, and LWDA differed in ewe lambs experiencing a positive or negative reproductive outcome.;There was no significant effect of nutritional treatment or progesterone pretreatment on overall fertility in any replicate. In replicate 1, Higher lambing rates were observed in ewe lambs in the H than in the L ADG category (P=0.01). Ewe lambs that were heavier at breeding and had a higher LWDA had greater reproductive outcomes. In replicate 2, ewe lambs in the M but not H ADG category had or tended to have higher conception rate (P=0.06), pregnancy rate to the first service (P=0.02), proportion lambing (P=0.03) and lambing rate (P=0.06) than L ADG animal lambs. Reproductive outcomes increased with increasing LWDA for most response variables. In the pooled replicate, most reproductive performance variables were higher (P<0.01) in the H compared to the L ADG category. Ewe lambs in the H breeding weight category had higher (P<0.01) reproductive responses than ewe lambs in the L and M with ewe lambs in the M category having intermediate values. Ewe lambs in the H and M categories lambed for the first time at a younger age than ewes in the L category (P<0.01). Reproductive response variables increased with increasing weight day averages in most response variables, and the age at first lambing was lower in ewe lambs in the H compared to the L LWDA category (P<0.001). Breeding weights, ADG, and LWDA were significantly higher (P<0.05) in ewe lambs with a positive compared to a negative reproductive outcome for estrous response, conception rate, pregnancy to the first service, overall pregnancy rate, proportion lambing, and lambing to the first service period. Average daily gains (169+/-44 v 114+/-12 v 85+/-5 g), breeding weights (61+/-5 v 51+/-1 v 44+/-1 kg), and LWDA (227+/-18 v 189+/-5 v 167+/-2 g) were significantly higher (P<0.05) in ewe lambs having triplets and twins compared to singletons.;Increasing the level of nutritional supplementation, ADG, and LWDA can impact fertility, and sufficiently supplementing ewe lambs may allow an advanced estrous response and pregnancy to first service without relying on progesterone pretreatment.

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