Effect of feeding level and diet type on the performance of crossbred suckler cows and their calves

A 2x2 factorial design experiment with 32 spring-calving Hereford-Ayrshire and 31 Limousine-Ayrshire suckler cows was conducted to compare the effects of diets based on hay (H) or urea-treated straw (US) at two feeding levels (moderate; M and low; L) on the performance of cows and their calves. For feeding level L, the amount of feed was restricted to 70% of that for feeding level M. Diet H was based on hay while for the US-diet, hay was replaced by urea-treated straw and barley (M:1.1 and L:0.8 kg dry matter, DM/day/animal). Urea-solution was included in the H-diet to balance protein intake with respect to US-diets. Untreated straw was also offered on all diets. Feeding pre partum commenced by offering 1.0 kg/day of a barley-rapeseed meal mixture from day 60 to 30 and 1.5 kg/day from day 30 to 0 pre partum. Post partum cows received 3.0 kg/day of the same mixture. All cows were in calf to Charolais sires. During the mating period, cows were inseminated after oestrus synchronisation and subsequently exposed to a bull. Average daily intakes of the cows were on treatment MH 9.1 kg DM/day and 77.4 MJ metabolizable energy (ME), on treatment MUS 8.5 kg DM and 67.2 MJ ME, on treatment LH 6.9 kg DM and 58.9 MJ ME and on treatment LUS 6.7 kg DM and 53.7 MJ ME, respectively. Live weight gain (LWG) during the indoor feeding was lower (P<0.01) for cows on feeding level L than M. Cows fed US-based diets lost more (P<0.05) live weight (LW) during indoor feeding than those based on II-diets. Cows replenished LW losses at pasture and there were no differences in LW between treatments at the end of the grazing season. Imposed feeding treatments and the sex of the calf had no affect on the incidence of calving difficulty. There were no significant treatment effects on calf LWG or suckler cow milk production. During mating 69.3% of all experimental cows successfully conceived. The low level of feeding had no adverse affects on cow or calf health, but depressed reproductive performance. Cows replenished LW losses during the grazing period on sufficient good quality pasture. Urea-treated straw proved to be a suitable winter feed for spring calving suckler cows.