Abstract:
Crossbreeding is found in almost all sectors of agriculture, including maize cultivars, poultry, pigs, small and large livestock breeds. Dairy has traditionally been one of the last strong holds of pure breeding strategies for Holstein, Jersey and Ayrshire. New Zealand was one of the first countries to adopt crossbreeding on a commercial scale by supplying semen from crossbred bulls for artificial insemination. Interest in crossbreeding is often due to concern with the depreciation of secondary, or management traits and is a relatively simple method to reduce inbreeding depression, introduce favourable traits from complementary breeds and take advantage of heterotic effect in several traits. Many South African dairy farmers have adopted the pasture-based and seasonal farming system, practicing criss-cross breeding between Holstein-Friesian and Jersey sires. Crossbred KiwiCross™ semen from New Zealand became available to these farmers, however, a Biological Impact Assessment study was requested by Government as a prerequisite to importing KiwiCross™ semen into South Africa. Individual cow performance data were recorded from six dairy farms in KwaZulu-Natal that were using KiwiCross™ sires alongside Holstein-Friesian and Jersey sires from LIC New Zealand. There were official milk (INTERGIS) records on 148 Holstein-Friesian, 80 Jersey, 476 KiwiCross™ and 287 non-descript sired heifers, and all were born in 2014. Records comprised of milk production, somatic cell count, inseminations, calving and visual inspection data. Mean lactation milk yield was not significantly different (P>0.05) between KiwiCross™, Holstein and non-descript breeds. The three sire breed groups, however, produced significantly higher (P<0.05) milk yield than the Jersey. There were no significant differences (P>0.05) in somatic cell score among the four sire breed groups. Lactation yields of milk, fat and lactose were significantly lower (P<0.05) for the Jersey compared to Holstein, KiwiCross™ and non-descript breeds. For protein yield, a significant difference (P<0.05) was only observed between the KiwiCross™ and non-descript, with the KiwiCross™ having the highest and non-descript the lowest lactation yield. Age at First Calving was significantly higher (P<0.05) for the KiwiCross™ compared to Jersey, Holstein and non-descript breeds. Services per conception were significantly higher (P<0.05) for the non-descript than the KiwiCross™, Holstein and Jersey. Analysis of the production and fertility data, along with linear visual inspection yielded results similar to what is seen in other international studies, i.e. crossbred animals raised in pastural systems produce production figures comparable with Holstein-Friesian and significantly higher (P<0.05) than Jersey pure breeds while showing slightly higher values in reproduction, health and welfare traits.
