MMN March 2025 – The Multiple Roles of Methionine

Methionine is an essential amino acid for dairy cows and is the first limiting amino acid for milk production, followed by lysine. Typically miking rations are deficient in methionine, with feed ingredients containing low levels. There are several benefits of methionine supplementation for both milking cows and dry cows over the calving period.

As dairy cows are unable to produce sufficient quantities of methionine in the rumen to meet their requirements, supplementation is necessary. Even if high levels of protein are fed, methionine is still likely to be deficient. Methionine is normally supplemented in a rumen-protected form, so that it is not degraded by the rumen microbes. It can then be easily absorbed in the small intestine, into the circulation and go on to provide multiple benefits.

By meeting the cow’s requirements for methionine, more milk will likely be produced with a higher fat and protein content, alongside improved metabolic health (liver function) and enhanced fertility. There are also improvements in nitrogen efficiency, meaning that lower protein diets can be fed, potentially allowing a cost saving. The improvement in nitrogen efficiency means that milk urea levels may drop when feeding protected methionine.

Methionine has been shown to enhance liver function over the transition period, reducing the build-up of fat in the liver. It also has a role in immunity, helping reduce oxidative stress as methionine is required for the synthesis of glutathione, a powerful antioxidant and one of the most prevalent antioxidants formed in the liver. Some studies have shown a lower somatic cell count in cows supplemented with methionine.

The benefits of feeding methionine are greatest when provided in the latter part of the dry period (last 21 days) and in early lactation. During lactation, the biggest responses are seen during early lactation, and as lactation progresses, the responses in milk yield and composition tend to decline. This effect is down to the transition and early lactation period being the time of greatest nutrition demand and metabolic stress, with the need for amino acids, particularly methionine, at its highest. This is when supplementary methionine can help bridge the gap between dry matter intake and nutritional demand (supplementation during the dry period has been shown to increase dry matter intake after calving). Once the cow has recovered from negative energy and protein balance in early lactation, the response to supplemental methionine is less, as demand reduces, and cows are more able to meet their nutritional requirements.

A meta-analysis reviewing 21 publications on the effects of rumen protected methionine supplemented before and after calving showed that supplementation pre-calving had no significant effect on dry matter intake in the dry period. However, after calving, dry matter intake, milk yield, milk fat yield and milk protein yield all increased, as shown in the following table:

 The effect of supplementary rumen protected methionine pre- and post-calving on dry matter intake, milk yield and milk composition post-calving

	Control - no methionine	Response to methionine supplementation
Dry matter intake (kg/day)*	19.5	+0.45
Dry matter intake @21 DIM (kg/day)		+1.38
Milk yield (kg/day)*	35.6	+0.8
Milk yield @ 21 DIM (kg/day)		+2.13
Milk fat (g/day)*	1288	+75.8
Milk fat @21 DIM (g/day)		+117.6
Milk protein (g/day)*	1032	+43.4
Milk protein @21 DIM (g/day)		+92.1

*Dependent on the duration of measurement which averaged 85.9 days (±38.36SD)

Source: Zanton & Toledo 2024

The increase in milk fat percentage and milk protein percentage with supplementation was +0.15% and +0.66% respectively. It was found that the response to methionine fell as lactation progressed and it was concluded that supplementation both before and after calving had a greater effect on production compared to just feeding methionine in lactation alone.

The recommended intake of methionine is often declared as a ratio with lysine, with the target being a 3:1 lysine to methionine ratio for milking cows. In terms of % of metabolisable protein, the target for methionine is 2.4% and lysine 7.2% to optimise milk yield and milk protein synthesis (NRC 2001). Therefore the level of supplementary methionine will vary depending on the ration. For dry cow diets, the ratio should be lower, with a ratio of 2.8:1 recommended. For close-up dry cows the target intake is between 30-35g methionine and 90-95g lysine. It may be worth speaking to your nutritionist about rumen protected methionine and how it can be incorporated into the dry and milking cow rations.

Reference: G.I. Zanton and M.Z. Toledo. 2024. Systematic review and meta-analysis of dairy cow responses to rumen-protected methionine supplementation before and after calving. Journal of Dairy Science Communications. Vol 5, issue 4, pp293-298.

lorna.macpherson@sac.co.uk; 07760 990901