Milk production and survival of spring-calving carryover cows in New Zealand dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand
dc.contributor.author | Gardner, Rachel | |
dc.date.accessioned | 2017-11-05T22:03:53Z | |
dc.date.available | 2017-11-05T22:03:53Z | |
dc.date.issued | 2017 | |
dc.description.abstract | Non-pregnant cows are generally culled from dairy herds and replaced with two-year-old 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. In this study, calving interval was used as a tool to identify and define the carryover cow population in spring-calving dairy herds. Linear modelling methods were used to compare carryover cow milk production with that of heifers, lactation-matched and age-matched non-carryover cows. Lastly, the survival for second-lactation carryover cows was compared with that of two-year-old heifers and lactation-matched non-carryover cows. Results showed that annually, 2.5% of spring-calving cows had returned to a milking herd after a carryover period in the previous year. Of those carryover cows, 43% returned to a milking herd at four years old, after failing to conceive in their first lactation. Most (69%) dairy herds contained less than 5% carryover cows and 17% of dairy herds comprised of zero carryover cows. The difference between the proportion of Holstein-Friesian in the carryover cow and non-carryover cow group was minimal (2%) but statistically greater (P<0.01) for the carryover cow group. Estimated breeding values (EBVs) for milk traits (milk yield, fat yield, protein yield and somatic cell count) were greater (P<0.01), but fertility EBVs were lower (P<0.01) for the carryover cow group in the year when they failed to conceive, compared to those for the non-carryover cow group. These were reflected in greater (P<0.01) selection indices (Breeding Worth and Production Worth) for carryover cows. After the carryover period, EBVs for milk traits and fertility decreased, and Breeding Worth was lower (P<0.01) for the carryover cow group, compared to the non-carryover cow group. Carryover cow milk yield, fat yield, protein yield and somatic cell score was greater (P<0.01) than those for heifers, lactation-matched and age-matched non-carryover cows in their first carryover year. This milk production advantage was maintained for up to three carryover years, if the carryover cow maintained an annual calving pattern, but at a decreasing rate. The probability of survival (days) was lower (P<0.01) for second-lactation carryover cows when compared to heifers and lactation-matched non-carryover cows. These findings are important for the New Zealand dairy industry as they can aid on-farm culling (removal from the herd) decisions. | en_US |
dc.identifier.uri | http://hdl.handle.net/10179/12234 | |
dc.language.iso | en | en_US |
dc.publisher | Massey University | en_US |
dc.rights | The Author | en_US |
dc.subject | Dairy farming | en_US |
dc.subject | Management | en_US |
dc.subject | New Zealand | en_US |
dc.subject | Milk yield | en_US |
dc.subject | Dairy cattle | en_US |
dc.subject | Reproduction | en_US |
dc.subject | Research Subject Categories::FORESTRY, AGRICULTURAL SCIENCES and LANDSCAPE PLANNING::Animal production::Animal nutrition and management | en_US |
dc.title | Milk production and survival of spring-calving carryover cows in New Zealand dairy herds : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Animal Science at Massey University, Manawatu, New Zealand | en_US |
dc.type | Thesis | en_US |
massey.contributor.author | Gardner, Rachel | |
thesis.degree.discipline | Animal Science | en_US |
thesis.degree.grantor | Massey University | en_US |
thesis.degree.level | Masters | en_US |
thesis.degree.name | Master of Science (MSc) | en_US |
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