Abstract
Profitable milk production and genetic improvement in dairy herds depend largely on fertile cows calving annually to initiate a new lactation period. Over the last 30 years, several studies have indicated a decline in the reproductive performance of dairy cows. From the perspectives of many farmers and veterinarians, the reproductive performance of cows is related to the calving interval (CI) and services per conception (SPC). Using these traits as cow fertility indicators is problematic as CI is dependent on subsequent calving dates, while SPC is strongly linked to inseminator proficiency. Cow fertility refers to the ability of cows to come into oestrus soon after calving, to conceive from a minimum number of services, and to stay pregnant until the next calving. In this paper, non-genetic factors affecting fertility traits other than CI in Holstein cows are discussed. Service records (n = 69 181) and pregnancy check results of 9 046 cows in 14 herds were available. Six fertility traits were derived. Means (± sd) for the interval traits, namely calving to first insemination (CFS) and the interval from calving to conception (days open (DO)) were 77 ± 30 and 134 ± 74 days, respectively, while the number of SPC was 2.55 ± 1.79. The proportion of first services occurring within 80 days post partum (FS80d) and the proportion of cows being confirmed pregnant within 100 days (PD100d) and 200 days post partum (PD200d) were 0.64 ± 0.48, 0.36 ± 0.48 and 0.71 ± 0.45, respectively. While lactation number, calving year and calving season affected reproduction traits significantly, herds (management) had the largest effect.Keywords: Dairy cows, days open, interval to first insemination, reproduction
Highlights
Profitable milk production and genetic improvement in dairy herds depend on fertile cows calving annually to initiate a new lactation period
Fertility traits were derived that measure the ability of cows to show heat early in the breeding period and the probability of the success of insemination and confirmation of pregnancy. These traits included the interval from calving date to first service date (CFS), the interval from calving date to conception date or days open (DO), the number of services per conception (SPC), whether cows were inseminated within 80 days post partum (FS80d), and whether cows became pregnant within 100 days (PD100d) and 200 days post partum (PD200d)
This is to be expected as the observed values for these traits are the result of a complex interplay among elements such as the decision policy of the dairy farmer for the voluntary waiting period (VWP), postcalving treatment of cows, nutritional management, environmental factors and the genetic merit of cows for fertility
Summary
Profitable milk production and genetic improvement in dairy herds depend on fertile cows calving annually to initiate a new lactation period. In South African Holsteins, the calving interval (CI) increased from 386 days in 1986 to 412 days in 2004 (Makgahlela, 2008) It seems that selection for higher milk yields has led to a decline in the fertility of dairy cows because of the unfavourable genetic correlation between yield and fertility (Pryce et al, 2004). This is done only after considerable effort has been put into getting cows pregnant This commonly includes a large number of inseminations, fertility hormone treatment sessions and natural service by a home-bred bull. This usually results in a protracted interval from calving to conception, leading to a high CI
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