Impact of forage quality and heat stress on milk composition and cheddar cheese yield

Abstract

The experiment assessed the effects of forage quality and heat stress on milk composition and Cheddar cheese yield efficiency. The experimental design was a 4 x 4 latin square, with 7-day adjustment periods followed by 5 days of sample collection. The treatments were: 1) high quality lucerne chaff-based diet plus cooling (sprinkler and shade) (HD+C), 2) high quality lucerne chaff-base diet without cooling (HD-C), 3) low quality lucerne chaff-based diet with cooling (LD+C), and 4) low quality lucerne chaff-based diet without cooling (LD-C; control). Animals were restricted to the same forage intake as the control treatment, and they all received 4.2 kg concentrates daily. Diets were fed in the form of total mixed rations and were balanced for protein using cottonseed meal. Cooling reduced body temperature by 1°C and increased milk yield by 0.5 L/day/cow (P< 0.05). Milk fat plus casein contents were affected by a combination of diet and cooling (P<0.05). The proportion of α_s2-casein in the total casein increased from 7.9 to 8.7% for the control and cooling treatments, respectively (P< 0.05). Cheese yield efficiency (i.e. adjusted cheese yield per 100 kg milk divided by theoretical yield x 100) for the HD+C treatment was greater by 1%, 5% and 9% compared with HD-C, LD+C and LDC treatments, respectively (P< 0.05).