Weight loss post-calving is almost inevitable in dairy cows. There is an ‘energy gap’, when feed intake can’t provide the energy required by milk yield after calving. This period of negative energy balance (NEB) lasts for at least 50 days after calving (Roche et al., 2009; Buttchereit et al., 2010). To meet the energy demands of milk production, cows must mobilise (break down) body tissue. Cows mainly use adipose tissue (fat), which supplies fatty acids (NEFA) and glycerol, as an energy source. In addition, muscle is mobilised for the first 2-3 weeks after calving; this provides amino acids, which can also be used for energy. Mobilising body tissue causes the weight loss seen post-calving.
We can assess how much body tissue is being mobilised in a variety of ways. Levels of NEFA in blood measure the degree of fat mobilisation, and levels of beta-hydroxy butyrate (BHB) in blood (or milk) measure to what degree NEFA are metabolised to ketone bodies, which are also used by the cow as an energy source. Measuring NEFA and/or BHB gives an indication of the cow’s metabolic status at the time of sampling. Several studies have correlated high levels of NEFA and BHB with increased risks of metabolic disorders, poor fertility and lower milk yield (Ospina et al., 2010a and b; Suthar et al., 2010; Raboisson et al., 2014).
Milk recording data (milk fat, protein, fat:protein, as well as more recently, fatty acids and MIR analysis) can be used to measure energy status of individual cows and/or the whole herd to review performance in the recent past.
Measuring body condition score (BCS) change in the weeks after calving demonstrates how much body tissue has been mobilised. Increased BCS loss post-calving is associated with poorer fertility (Butler and Smith, 1989; Roche et al., 2007); thinner cows (including as a result of increased BCS loss post-calving) have a higher risk of lameness (Bicalho et al., 2009; Randall et al., 2015) – see links on fertility and lameness. It is recommended that BCS loss in the 2 months after calving is limited to a maximum of 0.5 units.
Glycal Forte® has been shown to reduce BCS loss post-calving in a trial carried out on 90 cows in a high-yielding (>10,000 litres) UK dairy herd:
Cows in the Glycal Forte® group lost significantly less BCS in the 120 days after calving than the control group (P = 0.030). In addition, farmers who have fed Glycal Forte® to their close-up dry and fresh cows typically comment that they see less weight loss after calving. Several commercial farm studies have shown an improvement in fresh cow energy status when cows are fed Glycal Forte®.
How does Glycal Forte® reduce BCS and weight loss after calving? Glycal Forte® has a positive effect on energy balance in several ways.
Firstly, via its effect on rumen pH. Dairy cows undergo a period of rumen adaptation after moving from a less energy dense dry cow ration to a more energy dense milking ration. It can take up to 6 weeks for the rumen to adapt and reach maximum ability to absorb volatile fatty acids, which are the products of rumen fermentation. Therefore, in the same way that NEB is almost inevitable in dairy cows, so for about a month after calving, as these acid levels build up in the rumen, cows are inevitably at high risk of low rumen pH or sub-acute ruminal acidosis (SARA) (Humer et al., 2018). There are four effects of low rumen pH on the cow’s energy balance; these are:
The effect of Glycal Forte® on rumen pH post-calving was also demonstrated in the trial referred to above:
In addition to the effects of rumen pH on energy status, Glycal Forte® supplies bypass glycerol, from the proportion of the complex, which dissociates in the abomasum. Glycerol released in the abomasum is used metabolically more efficiently than glycerol released in or delivered to the rumen (Piantoni and Allen, 2015).
