The generally low reproduction rate of South African cattle has drawn attention to meticulous management and effective feeding programmes that will allow animals to produce in accordance with their genetic potential. A farmer’s income is largely determined by reproduction rate, the replacement rate in the herd, and the percentage of surplus animals available for marketing.
For any production system, there are a few criteria that must be clearly defined to ensure success. Among these, the producer needs to focus on weaning percentage – the weaning percentage of the cow herd should not be less than 85%. However, the reconception rate of first-calvers is a challenge, resulting in weaning percentages of less than 60% being recorded for this group. On average, the inter-calving period of South African herds are more than 400 days. The aim should be to have all animals reconceive within 82 days after calving to reach the 365-day inter-calving period target.
Other than genetics and the management of the herd’s genetics, nutrition remains one of the most manageable aspects when it comes to reproduction. An important point to bear in mind, however, is that no single nutrient can dramatically increase reproduction. The emphasis should always be on a continuous, balanced nutritional programme, which should be monitored against production responses and by using management tools such as body condition scoring.
One of the major causes of poor fertility in any production system is an energy deficiency and its balance in relation to protein and other nutrients. Energy is important for growth and sexual maturity, follicle development and ovulation, oestrus and maintenance of the placenta and other related organs during gestation. Energy imbalances often lead to metabolic disturbances, which in turn can lead to abortions and/or poor calf survival.
Influence of protein
Similarly, protein influences the growth and maturation of the reproductive organs as well as the animal’s endocrine system. Animals must therefore be fed in accordance with their protein requirements; it is advisable to manage heifers as a separate herd from the cow herd.
Heifers have an additional growth requirement and should be fed a higher protein feed or supplement. Their body weight and body condition should be carefully managed to ensure they are fully grown but not obese at first calving. Excessive energy intake, especially during the last trimester, must be prevented. In addition, protein quality is vital and NPN (urea) must not exceed 30% of total protein intake.
Although several minerals are directly or indirectly involved in reproduction, the following are singled out:
- Phosphate (P) deficiencies lead to poor, suppressed or irregular oestrus (heat) due to malfunctioning ovaries. It is also directly linked with the animal’s energy metabolism. Excessive calcium (Ca) intake in areas with brackish soil or water will lead to a P deficiency, as it is excreted by the kidneys together with the excessive Ca. The recommended ratio of Ca:P is therefore at least 1.5:1 to 2:1.
- Salt (NaCl): When ruminants have not had access to sufficient amounts of salt for long periods of time, they develop a salt hunger that can adversely affect fertility and cause retained placenta problems.
- Magnesium (Mg): Subclinical magnesium deficiencies sometimes occur under grazing conditions and have a definite influence on reproduction via the various functions of Mg in the body. Magnesium deficiencies are often an induced deficiency due to over-fertilisation of K and N or high levels of Ca and P in the diet, which then lowers Mg absorption.
- Copper (Cu) deficiencies can result in prenatal deaths, especially during the early embryonal stage, as copper is present during embryo implantation. As in the case of Mg, induced Cu deficiencies will occur as a result of imbalances with molybdenum, zinc, sulphur and other antagonists. Semen quality can be affected in the case of serious deficiencies. Copper can lead to toxicity in sheep and Cu supplementation should therefore be closely managed.
- Zinc (Zn) is especially important for male animals and plays a significant role in the morphological processes of spermatogenesis. A deficiency can lead to low semen production and suppressed libido. Once again, the balance of nutritional elements is important and excessive Ca in the diet can lower Zn absorption from the digestive system.
- On the other hand, the effect of manganese (Mn) deficiencies is greater in female reproductive processes. The clinical symptoms of Mn deficiencies include poor, irregular oestrus coupled with low conception figures. As in the case of Mg, excessive Ca intake can inhibit Mn absorption and can lead to a secondary deficiency. Severe Mn deficiencies can have an adverse effect on male animals’ libido and spermatogenesis.
- Early births, poor viability, muscle dystrophy in severe cases, and low fertility in male and female animals are all symptoms of possible selenium (Se) deficiencies. Acute Se deficiencies are, however, uncommon and research has shown more positive than negative effects emanating from above normal Se supplementation, although these levels were still below toxic. The relationship between Se and vitamin E as antioxidants is well-known and has been the subject of numerous research studies.
- Cobalt (Co) has a dual function in reproduction. On an indirect level Co has a critical function in energy metabolism, as it forms the centre of the vitamin B12 structure, which in turn is involved in energy metabolism. There is also proof that Co deficiencies can have a direct influence on reproduction through its involvement in the reparation of the uterus post-partum and its support of oestrus (heat).
The role of vitamins
When looking at reproduction it is important not to lose sight of the role of vitamins. Vitamin A is known for its role in fertility, more specifically during the dry season when grazing is unable to supply sufficient levels of vitamin A. This is why vitamin A is administered in different ways at strategic times – from oral doses or injectable formats to licks. Vitamin E plays a lesser role but is important in its synergistic interaction with other nutritional ingredients such as selenium.
Importance of nutrients
It is clear that many nutrients are involved in reproduction, and that these elements should not be viewed in isolation. A carefully planned fodder flow programme is essential, especially during the critical 100-day period around calving.
As can be seen in Figure 1, during the critical 100-day period the nutrient requirements of the cows are extremely high, and the use of appropriate production supplements will be beneficial. After the critical 100-day period, a balanced nutritional programme needs to be followed and the animals’ body condition score monitored.
A planned and balanced nutritional programme is essential if production targets are to be achieved. Only by measuring success against certain critical production targets can the producer truly affect the herd’s performance.
For more information, contact Nutri Feeds on 018 011 8888 or visit www.nutrifeeds.co.za. – Dr Francois van de Vyver, Nutri Feeds