Dairy cattle

Genetic and non-genetic factors related to the conception rate at first service of dairy cows

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Abstract

Most dairy cows in New Zealand are scheduled to calve in early spring to match animal requirements with seasonal pasture supply. Typically, mating starts in spring, 83 days after the start of the calving period and lasts for 10 to 12 weeks. National targets are for 78% of the herd to be pregnant 43 days after the start of the mating period, which places strong emphasis on fertility. Conception at first service (COFS) is a key indicator of reproductive performance in dairy herds and can be influenced by multiple sources of variation. The present study evaluated the effect of genetic and non-genetic factors on the time from the start of mating to COFS (COFStime). Data from 5,057 spring-calving dairy cows from 3 dairy units in the Taupo area of New Zealand were collected during the 2023-2024 production season, including mating dates, daily body weight (BW) from walk-over scales, daily milk yield from milk meters, fat and protein percentages in milk from herd tests, disease events, and breeding values. Cows were artificially inseminated for six weeks, and a veterinarian confirmed the pregnancy status through ultrasound. Random regression models with Legendre polynomials on days in milk were implemented to model the trajectories of BW and milk production traits over lactation. A survival analysis was used to model COFStime as a function of farm, parity, proportion of Holstein-Friesian (PF), Holstein-Friesian×Jersey heterosis (HetFJ), fertility breeding value (BVfert), presence of disease events from calving to 30 days after first service, deviation from the median calving date, days from start of mating to first service, the relative change during the 21 days preceding the first service in fat and protein corrected milk production (ΔFPCM21d) and in BW (ΔBW21d). A significant effect on COFStime was observed for BVfert (pF or HetFJ (p >0.05). A hazard ratio of 1.13 was found for ΔBW21d, indicating that cows with a 1% BW gain during the 21 days preceding first service had a 13% higher hazard of conceiving at first service. A positive BW change in the three weeks before the first service indicates that the cow has recovered from the negative energy balance (NEB) typically experienced in early lactation. Prolonged NEB is known to impair metabolic pathways involved in follicular development, dominant follicle ovulation, and early embryo survival. The present results suggest that optimising feeding and management conditions in the three weeks before mating starts and during the whole mating period may increase the conception rate at first service in spring-calving grazing dairy cows.

Keywords: 2026

How to Cite:

Hickson, R., Jonker, A., Khan, A., Lopez-Villalobos, N., McNaughton, L., Rocha, J. & Tidey, C., (2026) “Genetic and non-genetic factors related to the conception rate at first service of dairy cows”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2286246. doi: https://doi.org/10.31274/wcgalp.23890

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