Milking cows for two consecutive years, with calving and mating occurring every second year, may exploit the superior lactation persistency of high yielding cows while improving reproductive performance. This study tested the feasibility of extended lactations in pastoral systems using divergent dairy cow genotypes (New Zealand [NZ] or Overseas [OS] Holstein-Friesian [HF]) and levels of nutrition (0, 3, or 6 kg concentrate DM/cow/day). Cows calved on 28 July 2003 and remaining cows were dried off by 6 May 2005. Of the 56 cows enrolled, 93% were milking at 500 days in milk (DIM) and 18% were milking at 650 DIM. Dietary treatments did not affect DIM (605 ± 8.3; Mean ± SEM), but there was a trend (P=0.09) for OS HF to have longer lactations than NZ HF. Genotype x diet interactions were detected for the total yield of milk and milksolids per cow, and as a percentage of liveweight. Differences between genotypes were greatest at the highest level of supplementation. Compared to NZ HF, OS HF produced 35% more milk, 24% more milk fat, 25% more milk protein, and at drying off had 1.9 units less body condition. Annualised milksolids production from NZ HF was 79% of a normal season’s production, compared to OS HF that produced 94%. Compared to NZ cows, OS cows had a similar 21-day submission rate (85%), a lower 42-day pregnancy rate (56% vs. 79%), and a higher final empty rate (30 vs. 3%) when mated at 451 days after calving. These results indicate that productive extended lactations up to 650 days are biologically possible on a range of pasture diets, and with appropriate cow genetics and feed management may ameliorate poor reproductive performance in high yielding dairy cows without sacrificing milksolids production.
Proceedings of the New Zealand Society of Animal Production, Volume 66, Napier, 245-251, 2006
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