Agri Kultuur November / November 2014 | Page 29

10 are, 236, 143 and 85 cows at culling rates of 20, 25 and 30%, respectively. To maintain a herd of 100 cows, the culling rate should not exceed 28%. Herds maintaining higher heifer survival rates show higher IHG rates at higher cull rates. Ways to reduce culling rates Cows are culled for a number of different reasons. In most cases cows are culled because of involuntary reasons. This may include factors such a poor milk yield because of poor genetic merit, cows failing to become pregnant, recurring incidences of mastitis, natural diseases, conformation traits and injuries. Good management would in many cases prevent cows being culled. Improving reproduction management would reduce culling rates because of infertility. Very few cows are inherently infertile and will get pregnant if serviced by a bull. When poor reproduction management intervenes, cows often do not conceive at all or have long open periods, i.e. the interval from calving to conception. Crossbreeding has been suggested as a way to reduce the reproductive performance of cows while also improving the survival of cows. Crossbreeding studies at Elsenburg A crossbreeding study is being conducted at Elsenburg comparing Holstein (H) and Fleckvieh x Holstein (FxH) cows with regards to milk production and reproductive performance of heifers and cows in a total mixed ration feeding system. Although other Simmental derived breeds like the Montbéliarde, from France, have been used in crossbreeding studies, the Fleckvieh, a true dual -purpose breed, has not been seriously considered in crossbreeding programmes. Generally crossbreeding is between major dairy breeds such as Jerseys on Holsteins to reduce live weight and to increase fat and protein percentages in milk. The Fleckvieh breed has medium to high milk yields with high milk quality traits. As the reproductive performance of heifers and cows affects their survival and cull rates, these traits were evaluated. It was found that FxH heifers were inseminated earlier than H heifers resulting in more cro ssbred heifers being inseminated for the first time by 14 months of age. Age at first calving was however similar for both breeds. Similarly FxH cows were inseminated earlier after calving than H cows with a larger proportion of FxH cows inseminated by 80 DIM. This resulted in FxH cows showing a shorter interval from calving to conception and a larger proHolstein Fleckvieh portion of FxH cows pregnant within 100 days after calving than H cows, being 0.29 vs. 0.45, respectively. The cull rate of the H and FxH herds also differed resulting in an increase in the number of cows in the FxH herd while the H herd showed a decline in herd numbers. At the start of the trial, 23 FxH and 22 H first lactation cows were included in the study. Bull calves were reared for either veal of beef while heifers were reared to be included in the two herds. At present the FxH herd consists of 70 animals, 34 heifers and 36 cows, while the H herd consists of 30 animals, 15 heifers and 15 cows. This means that while the FxH herd has increased in size by 9.4% per year, the H herd has declined by -5.3% per year. This change in IHG is reflected in the following figure using a standard herd size of 25 cows at the start of the trial. The difference in the value of the two herds at R8000 per cow amounted to R560 000 over the six year period in favour of the FxH herd. In closing Internal herd growth is highly correlated to dairy farm profit. Parameters required to estimate IHG include average cow culling rate, calving interval, age at first calving, survival of heifers from birth to first calving and bull to heifer ratio. Cows are culled for a number of different reasons. To determine ways to reduce culling rates, a list of animals leaving the herd (herd cull list) should be kept up to date. The list should contain the following information: cull date, name of the animal, its birth date, recent calving date, recent lactation number (zero for heifers), number of cows in the herd, the number of all heifers and cows in the herd and the cull reason. From these records, information on the age and lactation stage of cows at culling could be determined. Improving reproduction management would be one way to reduce culling rate as cows not becoming pregnant is one of the major reasons for cows being culled.