Improving Cow Health
31 July 2009
Optimal feeding and management of high producing dairy cows is essential if production potential is to be achieved without detrimental effects on cow health or welfare. High genetic merit cows can be considered akin to Formula 1 racing cars, requiring high quality inputs and monitoring for signs of malfunction if they are to perform to their capacity. Among the most common health disorders in dairy cows are lameness, acidosis, ketosis, fatty liver, displaced abomasum (DA) and mastitis.
Lameness is one of the most common conditions on dairy farms, with 25% of cows estimated to be suffering lameness at any one time i.e. up to half a million cows may be lame on any one day in the UK. It is estimated than the average case of lameness costs £172, with a reduction in future milk yield during that lactation of 390kg per 305-day lactation. Many factors are involved in lameness, such as poorly designed housing and fighting which cause cows to turn sharply and increase hoof abrasion. Recommendations are generally for wide feed passages (3 to 3.5 metres) and a minimum feed space of 0.6 metres per head for Holstein cows to reduce negative social interactions between cows.
Cubicle comfort is very important to reduce standing time on concrete and regular scraping is essential to reduce contact with slurry; contaminated slurry is one of the most significant risk factors for digital dermatitis. Lame cows also show reduced heat and recent research work has demonstrated that lame cows can be over 40 days later getting back in calf than healthy herd mates.
Nutritionally, there is a well-established link between lameness and diet. If inadequately buffered, high levels of starchy cereals can lead to reduced rumen pH and development of acidosis, whereas a rumen pH well above 6.0 is essential to ensure growth of the fibre-digesting bacteria in the rumen. However, levels of rapidly fermented cereals are normally increased during early lactation, at the expense of fibre, to achieve higher energy intakes thereby increasing the risk of acidosis. Acidic conditions in the rumen increase susceptibility to laminitis. High-energy, non-starch ingredients can be substituted for a proportion of the cereal component of the diet to increase energy density in a ‘safe’ manner. Megalac protected fat contains around 2.5 times the energy concentration of typical cereals and, as it is not fermented, does not increase the acid load in the rumen.
Ketosis and fatty liver are conditions which are common around calving and reflect inadequate energy supply and/or lack of particular energy sources. In simple terms, the huge demand for energy post-calving, coupled with limited feed intake, results in mobilisation of body fat for use as an energy source. In order to process this energy, the liver requires glucose which if insufficient, leads to the production of so-called ‘ketone bodies’ and/or a build-up of fat in the liver. Avoiding over-fat cows at calving, feeding high energy diets post-calving, and providing a source of glucose (e.g. starch) in the diet will help to limit the risk or extent of development of these disorders.
A further condition common in high producing cows is DA, with left DA accounting for around 85% of cases. There are many causes of DA but major dietary factors include a high rate of transfer of feed from the rumen to the abomasum, leading to accumulation of gas and poor motility of the abomasum; this can occur as a result of high concentrate, low fibre diets. Level of calcium in the diet is also important in the incidence of DA due to its role in muscle contraction.
Ensuring a sufficient level of calcium in the diet will not only help ensure optimal functioning of the abomasum, but will also reduce the incidence or extent of milk fever. Dietary fat, while primarily providing a source of energy, does not lead to production of gas and protected fats like Megalac also supply calcium which helps improve the mineral status of the animal.
Mastitis is one of the most prevalent infectious conditions on farms. The average incidence of mastitis across dairy farms is estimated at 27.4% with a range from 8.2 to 76.4% between the best and worst farms, and is estimated to cost the UK dairy industry £100 million per year. Milk production is typically reduced by 10 to 26% in udder quarters with subclinical mastitis, while fat is reduced by between 3 and 12% and solids-not-fat by between 3 and 11%.
Recent evidence has shown that mastitis also has a negative effect on cow fertility. Mastitic cows have a smaller ovulating follicle (which contains the egg) and an increased time to ovulation, potentially reducing accuracy of timing of insemination.
As with most conditions, there is no one single cause of mastitis and many factors are involved in its development. It is well known that under-nutrition, or imbalanced nutrition, impairs the immune system and increases susceptibility to infectious disease. Most udder infections occur around calving, and achieving high energy intakes to help maintain body condition score post calving and through early lactation can help reduce the level of stress high yielding cows may experience during this period. Protected fats can significantly improve energy density so that the cow can consume more energy in every bite at a time when dry matter intake is low and increasing only slowly.
High producing animals are susceptible to diseases and health disorders with multi-factorial causes. However, nutrition clearly plays a vital role in helping maintain a high health status within the herd. Particular ingredients or supplements can form an important part of the diet to assist formulation of rations which are balanced to meet the requirements of the cow while minimising potential negative issues.
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