A comparison of spring and autumn calving within two split calving herds
Bachelor of Applied Science (Honours)
2004
Lorna Tantrum
Abstract
In New Zealand milk production has a high peak in the spring time, with large
volumes produced daily in October to December, but very little milk produced in the
winter, which does not make efficient use of the dairy factories. Spring calving does
not always match the herds feed demand to the feed supply; on farms with dry
summers and warm winters split calving, with some cows calving in the autumn and
some cows calving in the spring, often matches the feed demand to the feed supply
more closely. In addition, some payment systems, e.g. winter premiums, encourage
farms to produce milk in a smoother lactation curve. However, it is possible that
cows that calve in the autumn may have reduced fertility. High fertility is needed on
New Zealand dairy farms as cows must become pregnant and give birth to initiate
lactation, and at the required time of year.
Two split calving farms were studied; one in the Manawatu, Massey University’s
No.1 Dairy (No.1), and one in Northland, Mt Moriah Jerseys Ltd (MMJ). The period
of the study was January 2003 to December 2003. The calving periods were longer in
the spring than the autumn on both farms. The autumn herd on MMJ had the highest
28 day calving rate (75%). In the autumn herds 11-18%, and in the spring herds 2528%, of the cows had calved less than 40 days before the mating period; these cows
were likely to still be anoestrus at the start of mating. On both farms the autumn
herds had higher submission rates than the spring herds. The non-return rates (NNR)
of the two herds on No.1 were the same (45%), but on MMJ the autumn herd had a
considerably higher NNR than the spring herd (70% compared to 40%). The MMJ
spring herd was the largest herd (201 cows), which may have reduced its fertility as
larger herds have been found to have lower conception rates. The autumn herd on
No.1 had the highest efficiency of oestrus detection (96%); the spring herd on MMJ
had the lowest (74%); this is defined as the number of normal cycles less the number
of double cycles over the number of normal cycles. The autumn herds had the highest
(No.1 - 32%) and the lowest (MMJ - 10%) incidence of health problems; this did not
seem to be associated with fertility.
No.1 had a very dry summer in 2003, and consequently had a lower pasture growth
rate than normal. Moreover, MMJ had a wet autumn, which was followed by a wet
spring reducing the pasture growth to below average. The proportion of
supplementary feed in the diet on No.1 was 20% and on MMJ was 38%. The
estimated pasture utilisation on No.1 was 67% and on MMJ was 69%. The milk
produced on No.1 and MMJ was approximately 77 and 90 kg MS/t DM feed eaten
respectively. No.1 produced 780kg MS/ha and 321kg/cow; MMJ produced 1344kg
MS/ha and 357kg MS/cow.
In conclusion, the autumn herds appeared to have better fertility than the spring herds;
the autumn herd on MMJ had the best fertility and the spring herd on MMJ had the
worst. Possible reasons for the low fertility in the MMJ spring herd are the larger size
of the spring herd, the low efficiency of oestrus detection and the high percentage of
cows that had not calved within 60 days of the start of mating.