Non-pregnant cows are generally culled from dairy herds and replaced with heifers. Alternatively, non-pregnant cows can be dried-off at the end of lactation, retained for one year (carried over), before being mated and returned to a milking herd in the following year. The aim of this study was to estimate the percentage of spring-calving carryover cows in New Zealand dairy herds and to compare their milk production with that of heifers, lactation-matched and age-matched non-carryover cows. Results showed that 2.5% of spring-calving cows had experienced a previous carryover period. The majority (43%) of carryover cows had failed to conceive during their first lactation. Most (69%) dairy herds contained less than 5% carryover cows and 17% had zero carryover cows. Second-lactation carryover cows produced 4778.1±6.3 L milk, 228.7±0.3 kg fat, 182.0±0.2 kg protein, and had a somatic cell score (SCS) of 6.31±0.01, which was greater (P<0.001) than the milk production of heifers that produced 3514.5±5.9 L milk, 168.3±0.3 kg fat, 134.0±0.2 kg protein, and had a SCS of 5.89±0.01. Carryover cow milk production was also greater (P<0.001) than that of lactation-matched and age-matched non-carryover groups. The results of this study will aid on-farm culling decisions.

RR Gardner, PJ Back, N Lopez-Villalobos, and LR McNaughton

Proceedings of the New Zealand Society of Animal Production, Volume 77, Rotorua, 3-7, 2017
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