Effects of protein meal supplements on the growth and reproduction of Hereford heifers and cows grazing a native grass pasture in the subtropics

Abstract

In the coastal subtropics of New South Wales, pasture growth occurs mainly in summer, when 500-600 mm of rain is expected. During winter, pasture quality declines, with digestible organic matter content as low as 374 g/kg DM in August and nitrogen down to 6.5 g/kg DM. Growth and reproduction of British breed cattle is also low so that, in an attempt to increase these attributes, protein meal supplements were offered to Hereford heifers and cows over 5 years. Heifers without supplements lost liveweight during their first winter and none calved after being mated at 15 months of age to Hereford bulls during a 9-week joining period. During their second winter, 58% of the heifers calved and, over 5 mating seasons, their mean annual calving rate was 48%. Supplemented heifers gained liveweight during their first winter and 95% of them calved, after first-joining at 15 months of age. Over 5 years their mean calving rate was 85%. Delaying first-joining to 27 months of age, as determined by a second group also supplemented with protein meal, did not increase production or mean calving rate (81%) over 5 years. The 230-day adjusted liveweight of calves weaned from non-supplemented heifers was 138 kg, significantly (P< 0.01) less than the 179 ¦10 kg (mean ¦ s.e.d.) for calves weaned from the supplemented early-calving group, or 198 kg for the supplemented late-calving group. The results highlight the limitation to cattle production imposed by the low levels of nitrogen and poorly digestible pasture, and emphasise the important role of protein meal supplements with added minerals in increasing production of breeding herds grazing unimproved pastures in the subtropics.