Reproductive performance on the up and up

The highest 6-week in-calf rate and lowest not-in-calf rate on record for NZ herds was reported by LIC in April 2024. This is excellent news for farmers, as herds are more favourably placed for ongoing reproductive success next season, with cows calving earlier, more early season days-in-milk and greater opportunity to improve herd quality through culling options this autumn.

A compact calving pattern is central to sustainable herd reproductive performance in block calving systems. Dairy Australia and Dairy NZ’s InCalf key performance indicator of ‘6-week in-calf rate’ reflects the importance of this concept, measuring the percentage of the herd that conceive within the first 42 days of the mating block.

In block calving herds, there is only 12 weeks between planned start of calving and the start of the subsequent mating period. During this window, cows must calve down, recover and resume cycling to be ready for mating by the mating start date.

Earlier calving cows enjoy more recovery time, giving them a clear advantage over their later-calving herd mates. This translates into higher 3-week submission rates, conception and 6-week in-calf rates and greater mating success, as can be seen in Figure 1.

Chances to conceive are limited to a maximum of four in most NZ block calving herds; some late calving cows may only get one or two mating opportunities before mating end!

The InCalf target is to have less than 13% of the herd left to calve 42 days in from the planned start of calving. The subsequent mating period target is to have 78% of the herd in-calf again after 6 weeks of mating.

6-Week In-Calf Rate by Calving Pattern Group v2
Figure 1. Impact of calving pattern on subsequent 6-week in-calf rate. NZ Herd Fertility Study, 2013. Source: LIC, 2013

New Fertility BV model in BW

NZAEL introduced a new fertility model to Breeding Worth (BW) in December 2023. This conception date-based model puts the focus firmly on the first 6 weeks of a herd’s mating period. The breeding value definition, ‘Pregnancy Rate 42’, reflects the proportion of an animal’s progeny expected to conceive in the first 42 days of mating and aligns to the industry KPI of 6-week in-calf rate. It focuses on underlying female fertility, independent of gestation length effects on calving date.

The new model resulted in a lift in the average fertility BV across all breeds and some re-ranking of bulls. Your LIC breeding advisor will look at bull fertility BVs in the context of the updated breed averages, as they work with you to select the best bulls for your herd.

Interim 2023 NZ herd reproduction results

The highest 6-week in-calf rate and lowest not-in-calf rate on record for NZ herds was reported by LIC in April 2024. The interim Spring 2023 mating period results saw the average 6-week in-calf rate sitting at 69.3%, up 2.7% compared to 2022-23 (66.6%), while the not-in-calf rate has dropped to 14.9%. (Note: ‘not-in-calf rate’ is the percentage of cows without a pregnancy recorded against them in the database.)

This is excellent news for farmers, as herds are more favourably placed for ongoing reproductive success next season, with cows calving earlier, more early season days-in-milk and greater opportunity to improve herd quality through culling options this autumn.

NZ 6 week in-calf rate

LIC senior reproduction solutions advisor, Jair Mandriaza, comments “From a national level, these results are very impressive and have been welcomed after a couple of tough seasons. It seems many farmers have implemented improved management practices to overcome those tough seasons and, coupled with favourable weather in many parts of the country, are now reaping the rewards of their hard work.”

DairyNZ senior scientist Chris Burke said improved reproduction performance could also help farmers lower emissions. “Herd reproductive performance is key in ensuring dairy farming success and in lowering methane emissions by reducing the number of non-productive cows. These results highlight the ongoing sector-wide opportunities to help farmers improve animal efficiency and to continue working towards emissions reduction goals.”

Burke says the challenge for dairy farmers is to maintain this good performance.

“To lock in these gains, farmers should focus on hitting condition score targets at calving and on planning their spring feeding carefully.”

*Statistics collected from 4,699 seasonal calving herds across New Zealand with detailed InCalf Fertility Focus Reports, using data sourced from LIC and DairyNZ.

Read Eight key areas that impact reproduction for tips on how to improve reproductive performance on your farm.

by Michelle Lamerton
International Marketing Coordinator
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