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| Oklahoma State University researchers have studied the impact of short term energy restriction on ovulation rates of cycling replacement heifers. This trial is reported in the 2001 OSU Animal Science Research Report. The effects of acutely restricting nutrition on ovulation and metabolic hormones were evaluated in Angus x Hereford heifers. Heifers were housed in individual pens in a barn and fed a diet supplying 120% of their maintenance requirements for protein and energy (1.2 M) for 10 days to allow time to adjust to the environment and diet. Heifers were then fed a diet supplying either 40% of their maintenance requirements (.4 M) or 120% (1.2 M), and heifers were treated with prostaglandin so they would ovulate on day 14 of restriction. Seventy percent (7 of 10) of .4 M heifers did not ovulate on day 14 while all 1.2 M heifers had normal ovulation. Heifers fed .4 M had less plasma thyroxine and increased nonesterified fatty acid (NEFA) concentrations compared with 1.2 M heifers. Nutritional restriction decreased concentrations of insulin-like growth factor-I (IGF-I) in plasma. We conclude that acute nutritional restriction can alter plasma concentrations of NEFA, thyroxine, and IGF-I and induce anovulation in beef heifers. Restricting nutrient intake for 14 days prevented ovulation in beef heifers without altering body condition. Heifers should be managed to avoid short-term nutrient restriction to maintain normal estrous cycles. | |