Effects of post-partum supplementation on fertility of Bos indicus cross first calf cows

Prolonged post-par-turn anoestrous (PPA) interval is an important contributor to low fertility of Bos indicus cross cows in northern Australia (Entwistle and McCool 1991). The present experiment examined the effect of increased nutrition post-par-turn on the PPA interval of lactating first-calf cows grazing wet season pasture in the vegetative stage of growth. Pregnant Bos indicus x Shorthorn heifers, initially 24-30 months, were allocated by stratified randomization to 6 x 100 ha paddocks at Swan’s Lagoon from June 1993 until weaning in May 1994. The heifers calved from late October 1993 to December 1993, and were mated from January 1994 to April 1994. Supplement was fed twice weekly for 7 weeks at the rate of 21 kg/week.cow-calf unit to 3 of the 6 paddock groups from January to March 1994. The supplement consisted (kg/tonne) of cottonseed meal 660, cracked sorghum grain 250, Megalac rumen inert fat 70, calcium phosphate 8.5, limestone 8.5 and mineral premix 3. Liveweight (LW) and body condition score (CS) were measured each 6-8 weeks. Cyclicity of cows was determined by sampling for plasma progesterone at lo-day intervals during mid-January, early March and early May. Pregnancy status and time of conception were determined by rectal palpation. Treatments were compared by analysis of variance within which paddock groups were considered as the experimental unit.