Seasonal changes in body weight and condition, and pregnancy and lambing rates of sheep on endophyte-infected tall fescue in the south-eastern United States

Abstract

The objective of these studies was to evaluate the seasonal maintenance of body weight (BW) and condition, signs of fescue toxicosis, and reproductive performance of straightbred and cross-bred hair sheep grazing tall fescue or bermudagrass forage. Breeds examined were St. Croix (SC), Romanov (ROM) and cross-bred ewes. BW was measured in the summer (1998–2000) and the fall (1999) on ewes grazing bermudagrass overseeded with ryegrass (BER) or tall fescue (FES) forage. Body condition score (BCS) and serum prolactin concentrations were determined in the summer (1999, 2000) and fall (1999). Pregnancy and lambing rates of a summer and fall (1999) breeding season and pregnancy rates of the spring (2000) breeding season were recorded. BW and BCS reflected seasonal differences related to the forage availability of BER and FES, seasonal variations in toxins of FES forage and breed differences. At all times, serum prolactin concentrations were reduced in ewes grazing FES pastures ( P<0.01), with the exception of the summer of 1999, where cross-bred yearling ewes maintained on FES exhibited an increase in prolactin level compared to those grazing on BER forage (forage×breed; P<0.05). Pregnancy and lambing rates were similar for forage treatments, with the exception of a reduction in reproductive rate in yearling cross-bred ewes maintained on FES in summer (1999; P<0.05). Birth and weaning weights of lambs were similar for suckling ewes maintained on BER and FES forage. These experiments demonstrated that, in contrast to cattle, BCS of SC, ROM and cross-bred ewes can be maintained in an acceptable range with either BER or FES forage. Pregnancy rate may be reduced in yearling, but not the older ewes maintained on FES forage. Birth weights and growth of lambs of mature ewes were similar for the forage treatments. It is recommended that breeding of yearling ewes occur on pastures free of endophyte-infected tall fescue.