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The nutritional requirements of beef cows change as they proceed through different production phases. The supplementation of beef cows in terms of protein, energy, minerals (macro and micro), and vitamins is key when addressing these nutritional requirements, and will vary depending on the availability and quality of grazing.
A low body condition score (BCS) at the time of calving (less than three on the five-point scale) will extend the anoestrus period in cows. The anoestrus period has been defined as the period when the cow is recovering from calving and is not cycling. A cow that regains her condition late in the breeding season, will inevitably miss the breeding season or calve late in the following calving season.
Retain cows that calve
Important to note is that this effect is exacerbated in first-calvers, which can take up to 80 to 100 days to come into oestrous post-calving, whereas mature cows usually return to oestrous within 50 to 60 days. The aim of any beef producer should be to keep cows that calve each year, meaning they should return to oestrous as soon as possible, and be pregnant within 90 days of calving.
In addition, beef cows should maintain a BCS of 3,0 to 3,5 throughout the year. This can be achieved by managing the supplements cows receive during the various stages of production to minimise the risk of deficiencies.
The third trimester is undoubtedly the most important phase during pregnancy of the beef cow; however, little emphasis has been placed on the first and second trimesters due to their perceived ‘limited’ roles in calf development. However, nutrition during these phases will also influence the performance of the future calf. Restrictions in maternal nutrition will inevitably affect the development and future production potential of the calf, which will be discussed here.
Early to mid-pregnancy
The majority of the calf’s organs develop during early pregnancy and there are specific ‘windows’ when specific organs develop. Therefore, should cows experience nutritional deficiencies during early gestation (which coincides with the peak lactation period), not only will the suckling calf be at a nutritional disadvantage, but the future calf will be exposed to a developmental disadvantage as organ development may be restricted.
The nutritional requirements of cows peak at 60 days post-calving, however, intake is usually lower during this phase which leads to a negative energy balance in early to mid-pregnancy (zero to three months pregnant). Beef producers in South Africa generally opt to calve their cows during the rainy season when the most forage is available and hence supplementation rates would be lower compared to cows calving on dry grazing.
Calving when the most forage is available, allows the producer to rectify this negative energy balance during early to mid-pregnancy due to the higher quality of the forage material available. Therefore, cows generally regain some of their body condition during this phase. The only exception to calving during the rainy season is producers that have access to grain stover fields or irrigated pastures (which classify as good sources of food for cattle during the drier months), who calve their cows during the dry season.
Mid-pregnancy
During pregnancy, muscle fibres develop in two separate waves. The first wave takes place during mid-pregnancy (three to six months pregnant) and the second wave during six to nine months of pregnancy. The development of muscle fibres during these two separate waves will inevitably become the muscle potential of the calf in future. Should producers opt for calving during the rainy season, cows are generally in their mid-pregnancy phase on dry grazing, which is unanimous with low forage quality (high lignin content) and hence low protein supply.
Should cows not receive adequate quantities of supplemental protein, it means the cow will need to mobilise skeletal muscle tissue to meet the requirements of mid-pregnancy. Therefore, to support the first wave of muscle fibre development and ensure that condition is regained, cows should receive adequate quantities of protein from their supplements during mid-pregnancy, otherwise cows will lose body condition (in other words body mass) during this phase.
Late pregnancy
Muscle and adipose (fat) tissue development dominate the third trimester; therefore, this phase has the greatest impact on the future calf’s production tissues. After the calf is born, there is no increase in the number of muscle fibres, hence producers cannot rectify in-utero deficiencies to stimulate muscle fibre synthesis post-partum. In addition, adipose tissue development during this phase can affect the marbling observed in carcasses when carcasses are harvested.
Research demonstrated that cows experiencing a protein deficiency during late pregnancy (six to nine months pregnant) gave birth to bull calves with lower birthweights and in turn, had lower carcass weights at slaughter compared to those born to dams supplemented with protein. Similar results were observed in heifers. Heifers born to cows that received protein supplementation had higher weaning weights, higher 205-day weights, and attained puberty at a younger age than those born to dams that were not supplemented with protein.
The phased approach to the pregnancy of the beef cow has highlighted the importance of balanced nutrition and the lasting effects it can have on the calf crop. In essence, beef farming is a long-term operation and what is saved today, may cost you dearly in the future, so make wise decisions when it comes to the supplementation of your beef cows.
Table 1: Voermol Premix 450 (V4676) for different production phases of beef cows on dry grazing.
– Ashley Grimsell, technical manager, Voermol Feeds
For more information, send an email to Ashley Grimsell at ashley.grimsell@tongaat.com or refer to www.voermol.co.za
