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Sire selection to reduce the size of dairy cows

Sire selection to reduce cow size 1100 x 480

Recently, on social media, the size of dairy cows was discussed among dairy farmers. Most held the opinion that there are advantages to cows being smaller. It was suggested that smaller cows, on a daily basis, consumed less feed and had lower maintenance requirements than larger cows. However, while these opinions are technically correct, little was mentioned about that the fact that smaller cows produce less milk than larger cows. Comparing Holstein cows to Jersey cows complicates the matter further as Jersey cows, while consuming less feed per day, have a proportionally higher feed intake than Holstein cows, i.e. 4.0 vs. 3.4% of live weight. This because of the smaller size of the muscles and skeleton in Jerseys in comparison to Holsteins.

Large cows are a problem

Over the last 30 years, the milk yield per lactation of dairy cows has more than doubled. This was made possible using better genetic information about dairy sires and cows as well as better diets, housing, overall herd management aimed at improving the welfare of dairy cows. However, because of direct selection for higher milk yields, it has also resulted in cows becoming larger. Dairy farmers showing cows have also found that larger cows perform well in the show ring. For these reasons cows’ size has increased reaching a point where it should now be considered in the breeding objective of a dairy herd.

Larger cows create problems for dairy farmers having to keep cows inside intensive housing systems because of climatic conditions and space limitations. In some parts of the world it is too cold to keep cows outdoors during winter, while in other areas it is too hot. A larger number of cows can be kept using a housing system as only about 10 m² per cow is required. In an open camp system at least 100 m² per cow is required. Free stall cubicles inside housing systems designed for smaller cows are now, 30 years later, too small for larger cows resulting in injuries, cows not lying down in free stalls using the manure alleys which increases the risk for injuries, mastitis and feet and leg problems. For cows in pasture-based systems, walking long distances from the milking parlour to pastures and back, have created feet and leg problems resulting in higher than normal cull rates.

Sire selection

Sires selected for inseminating dairy cows determines the genetic progress of a dairy herd. Traits affecting the profitability of dairy cows should be considered when selecting sires. More than 30 traits are currently available on which sire selection can be based. This may include milk, fat and protein production, fat and protein percentages, functional traits (such as longevity, fertility, udder health, and calving ability), as well as health traits such as somatic cell counts, daughter pregnancy rate and productive life. Several conformation traits are also included in the genetic evaluation of sires.

Keep in mind that when selecting sires based on any number of traits, some traits may be linked. Other uncorrelated traits are also included in the genetic make-up of dairy sires. This means that when selecting a specific bull for insemination to improve the udders of dairy cows, it will also influence the milk yield, milk composition, body size and several other traits of his progeny. This may well mean that while improving the structure of the udder, milk yield may be reduced resulting in a lower income. This does not make economic sense. Using a mating programme would help towards a higher milk yield while also improving the udder structure of the progeny.

The small (~20%) positive genetic correlation between milk yield and live weight has resulted in the live weight (or body size) of dairy cows increasing over time. It would be better to use an index combining different economically important traits. Each trait also has a different heritability estimate resulting in differing genetic progress for each trait even though the breeder may be aiming to improve the production level or conformation traits.The full article is for subscribed members only. To view the full article please subscribe. It’s FREE!Log In Register

Author

  • Research Associate, Faculty of Animal Sciences, University of Stellenbosch

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