The effect of different protein supplements on the production economics and nematode resilience of merino ewes

Abstract

Ninety Merino ewes, divided into three equal groups, were kept on natural highveld grazing for 42 weeks. Group M received a mineral supplement continuously, averaging 28 g per day. The other groups received commercial protein supplements, group RDP a mainly rumen degradable supplement and group RUP, a mainly rumen undegradable supplement. These supplements had crude protein (CP) levels of 29% and 28% respectively and were supplied at strategic times during the reproductive cycle, at 250 g per ewe per day for 14 days before mating, at 350 g per ewe per day for 42 days, starting 21 days before lambing and at 500 g per ewe per day for 56 days, starting 21 days after lambing. Grazing was randomized to minimize differences in nutrition and parasite challenge, and had an average CP of 8.8%. Lambing rates were: RUP 96%, RDP 89% and M 76%. Lamb survival rates at 11 and 17 weeks post lambing were 75%&63% for RUP, 64%&57% for RDP and 55% and 48% for M respectively (P< 0.05). Wool production parameters were similar for all groups, as were mean faecal egg counts: 685 (RUP), 371 (RDP) and 465 (M). Body weights, body condition scores and FAMACHA scores were also similar for all three groups. Income per ewe, calculated at 11 and 17 weeks post lambing, was highest for RUP at R147.80&R132.87, lowest for M at R117.86&R111.13, and in between for RDP (R129.85&R121.38). However, the gross margin was the highest for M at both points (R114.35&R107.77) compared to RUP (R70.43&R54.93 – P < 0.03&P < 0.008 respectively), as well as RDP (R82.96&R74.12). Strategic supplementation with protein improved performance but the additional income was not sufficient to cover feed costs under prevailing conditions and neither supplement could therefore be economically justified.