Many cattle herds take a knock in winter when forage quality declines in the summer rainfall areas. Here are some strategies to improve forage utilisation and ensure maximum production efficiency.
A cow should produce a calf every year (365 days) and conceive again within 90 days after giving birth. To achieve this, the cow must be in optimal condition during the breeding season. (See Figure 1 below.)
Most farmers use body condition scores to rate the nutritional status of cows. The scores are based on a visual evaluation of how fat or lean animals are, on a scale from 1 to 5 or 1 to 10. A cow having a score of 1 would be dangerously underweight; while one with a high score would be obese. The ideal is to have cows score in the middle of the scales.
Underweight cows might have difficulty conceiving, but this would change if they gained weight. Fat cows usually have reproduction problems that, in most cases, are also the cause of their obesity. Cull these animals if they’re not producing offspring, as they’re only a burden to your farming operation.
Also read: The value of body condition scores
WHY USE SUPPLEMENTS?
The dry, pregnant period of cows is often neglected in the summer rainfall regions. In most beef herds, average body condition at the end of the winter isn’t what it should be because of the low quality of forage then.
Roughage is high in fibre, but low in crude protein and other nutrients. It is used as the main energy source to maintain body condition for most of the year, but often doesn’t satisfy the high energy requirements of cows.
Supplements can help to bridge the gap between nutrient supply and demand. Protein supplements, such as urea, oilcake and ammonium sulphate, are a cost-effective way to enhance forage utilisation and improve livestock performance, because it promotes greater roughage intake and/or digestion, and so improve the efficiency with which the cow uses energy from the grass.
Response to the supplement and the subsequent performance of grazing ruminants depends on the quality of the forage. As forage matures, its fibre content increases while the protein content decreases. Because of the high fibre content, cows take longer to digest old forage, eat less and subsequently have a lower energy intake than cows on better quality forage.
One study showed that it takes rumen microbes 83 hours to digest low-quality hay, compared to 55 hours for medium-quality and 41 hours for high-quality hay. Since the rumen is filled to capacity with most forage diets, any factor that speeds the passage of the diet through it will help the animal consume more feed.
Also read: How to establish forage crops and pastures
HOW MUCH SHOULD BE GIVEN?
Degradable Intake Protein (DIP) – not crude protein – has been identified as the first limiting nutrient for beef cows consuming low-quality, protein-deficient forage. DIP is the portion of the protein that’s broken down by bacteria in the rumen and is used as an essential nutrient to digest grass. Without DIP supplementation, cows won’t be able to use low-quality grass, and this will lead to a big loss in body condition, making them infertile and unproductive or, in extreme conditions, result in death.
Studies have consistently showed that DIP, regardless of the crude protein source or Undegradable Intake Protein (UIP) level, will significantly help to improve consumption of forage containing less than 7% crude protein. Once DIP requirements are met, additional supplements would result in wastage of crude protein, and this would reduce the potential cost to benefit ratio.
It was established that 4g total DIP/kg BW0.75 or 11% of the digestible organic matter in the forage, would be required to maximise total dry organic matter intake. (BW0.75 is the metabolic body weight of the animal = body weight to the power of 0.75.) This totals 390 g to 420 g DIP per cow, per day, depending on variables such as the size of the animal and forage quality. The DIP consumed through forage also needs to be accounted for to determine how much would be required from supplemental sources in a given situation.
UIP escapes the rumen degradation and reaches the small intestine in its original form, where it is absorbed for production. Supplementing this portion of protein is only necessary if higher production rates are required; for example, during lactation or growing.
Also read: Manage the rumen for profit
Nonprotein nitrogen (NPN) is a less expensive DIP source, but above a certain intake level may not be as efficient at stimulating forage digestion as supplements based on a proportion of the DIP coming from true protein.
Studies found that providing 80% to 85% of the supplemental DIP from urea (55 g to 65 g urea per cow, per day) in a winter maintenance supplement plus 120 g to 170 g oilcake (40% crude protein; 70% rumen-degradable) may be the most economical solution in South Africa, since a typical winter veld in this country contains 3% to 4% crude protein, 55% of which is rumen-degradable. Beef cows also typically consume about 2% (9 kg – 11 kg) of their body weight per day of low-quality forage if properly supplemented.
Whether total production costs will decrease by substituting dietary NPN for true protein sources depends on the effects on animal performance. Urea, for example, contains a nitrogen (N) equivalent seven times that of commonly used plant proteins such as sunflower meal and cotton seed meal. But, in addition to protein, plant sources also supply energy, vitamins and minerals that can contribute to improved animal performance.
Energy sources may not be necessary in winter supplements if maximum utilisation of low-quality grasses is the only goal. By maximising intake and digestion of low-quality winter forage with sufficient DIP there should be enough energy from the grass to maintain the body condition of dry, pregnant cows and to optimise reproduction during the wet summer season.
If the energy requirements of young, growing or lactating cattle exceed the energy that can be obtained from the forage at their disposal, additional energy will have to be supplied, either by changing to better quality forage or to a grain-based supplement. But remember that, unlike DIP supplements, grain supplements will have a negative effect on forage intake and digestion, especially if they provide more than 25% of the total diet, and depending on how low the forage quality is.
Energy supplementation, in effect, becomes a fine balance between optimising forage use and the level of animal performance to be achieved.
It doesn’t always mean protein supplements are economic for higher producing animals on low-quality forage. The most efficient supplement is the one that gives the greatest cost-effective feed conversion within a specific situation. Nevertheless, the forage-sparing effect of grain supplementation on stocking rate can sometimes be beneficial and must be considered in any economic analysis.
- This article was written by Dr. Hinner Köster and first appeared in Farming SA.