In farm animals early embryonic loss is recognised as a major cause of reproductive wastage. In sheep and pigs there is evidence that high energy intakes prior to ovulation and in early pregnancy depress systemic progesterone with a detrimental effect on embryo survival. The objective of this study was to investigate the effect of short term nutritional changes pre- and post-insemination on embryo survival and systemic progesterone in cattle. Preliminary results have been presented previously (Dunne etal., 1997).

Oestrus was synchronised in 247 beef cross heifers aged 18-24 months using two injections of prostaglandin (PG) administered 10 days apart. At the oestrus following the first PG injection heifers were allocated to either a Low (L, 0.6 M) or High (H, 2.3M) pasture allowance for the 10 day period prior to artificial insemination (AI). AI was carried out at the oestrus following the second PG injection using semen from a single Limousin bull. On the day following AI, heifers were randomly reallocated to either a L or H pasture allowance until embryo recovery at day 14 to 16 or pregnancy diagnosis at Day 30.