@conference {3672,
	title = {The percentage of spring-calving carryover cows in New Zealand dairy herds and their milk production, compared to heifers, age-matched and lactation-matched non-carryover cows},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {77},
	year = {2017},
	month = {06/2017},
	pages = {3-7},
	address = {Rotorua},
	abstract = {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{\textpm}6.3 L milk, 228.7{\textpm}0.3 kg fat, 182.0{\textpm}0.2 kg protein, and had a somatic cell score (SCS) of 6.31{\textpm}0.01, which was greater (P<0.001) than the milk production of heifers that produced 3514.5{\textpm}5.9 L milk, 168.3{\textpm}0.3 kg fat, 134.0{\textpm}0.2 kg protein, and had a SCS of 5.89{\textpm}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.},
	issn = {1176-5283},
	author = {Gardner RR and Back PJ and Lopez-Villalobos N and McNaughton LR}
}
