Beat the drop

With the 2023 calving season winding down on most farms, the focus will now switch to helping cows achieve a peak milk solid yield in the coming months. The payment system is focused on kilogrammes of fat and protein, and this is a function of milk yield and solids percentages. Previously, the solid percentages from the freshly calved cows in the herd would have been high, but now they will slowly start to decrease  and, after six weeks, they will serve as a true reflection of your herd health and the management practices carried out on your farm. With this in mind, the focus should not be on what the actual percentage of fat or protein is at the moment but, rather, the steepness of the decline. Protein will usually decline from March onwards as a result of a negative energy balance and dry matter (DM) intake. Butterfat percentages will drop from April onward or after the second round of grazing due to leafy grass and a high oil content in the grass. 

To ‘beat the drop’ it is crucial to focus on four key areas:

• Nutrition; 
• Rumen health;
• Grassland management; and
• Genetics.

Nutrition 

As mentioned previously, the first six weeks are vital in terms of setting the cow up for the rest of the lactation period. Achieving optimal cow nutrition is reliant on her dry matter intake, which will dictate the body condition score (BCS) of the cow and how long she spends in a negative energy balance. Aim to achieve an average BCS post-calving of more than 2.75, and avoid a drop of more than 0.5 units until breeding. Drops of more than 0.5 units are usually a symptom of reduced dry matter intake or, more importantly, a reduced energy intake. 

To calculate the potential or optimal intake of the herd, use this simple equation:

Peak yield (L)/1.5 = DM intake (kg)

e.g.: A herd peaking at 30L/1.5 = 20kg DM intake

Milk solid percentages will be determined by both the quantity and the quality of what is fed during early lactation. Milk protein levels will be determined by the starch and sugar content of the diet. Starch is usually provided in the form of concentrate, and sugar will come from grazed grass. With the weather in Ireland being as unpredictable as it is, both the starch and sugar content should remain as consistent as possible — whether that be indoors or outdoors. Butterfat percentages are determined by a lack of ruminal-degradable energy and the quality of the fibre presented to the cow. Increased levels of fatty acids in lush grazed grass must be counteracted with long fibre, like straw or grass silage. If this is not possible, then a high level of fibre should be included in the parlour nut, such as soya hulls, beet pulp or rolled oats.

Figure 1. Effect of Yea-Sacc supplementation or control on rumen pH (p<0.01).

Rumen health

When we talk about rumen health, we are talking about the bacteria in the rumen environment, which is mainly determined by the rumen pH. High amounts of concentrate or high levels of lush grass with a low fibre content create a toxic environment for the rumen bacteria, hampering them from breaking down feed efficiently and lowering the pH in the rumen. Once the pH falls below the optimal level of 6, the bacteria that help digest or ferment the feed inside the rumen will slow down and will not work as well. Another result of a reduced pH is damage to the rumen lining. This lining has both protective and absorptive functions. The cumulative result of a low rumen pH and poor rumen health is, ultimately, decreased performance and wasted nutrients from a diet that could potentially have encouraged the animals to perform much more successfully.

When cows are grazing — especially that second-rotation grass — we see a drop in butterfat, as most fats and oils found in plants are unsaturated, while the fats in milk and butter are saturated. 

Unsaturated fats are toxic to the rumen bacteria, and in order for them to survive, they go through a process called biohydrogenation. This process creates byproducts, which, in effect, stop the udder from producing butterfat. Grass, which can have especially high oil content in that late-spring/early-summer period, can cause this decrease in butterfat. The degree of the drop in butterfat is dose dependent, so the more oil in the grass, the greater the effect will be. Research has shown that the more leaf, or the “lusher” the grass is, the higher the fat content. Also, the more nitrogen we use in our pastures, the higher the fat content will be, amplifying the impact even more.

The signs of poor rumen health usually include poor rumination or chewing the cud, increased levels of loose manure and poor rumen fill. There is also a risk of increased levels of sub-acute ruminal acidosis (SARA) when cows are out at grass. There might not be any visual signs of SARA; sometimes, changes in the milk fat percentage are the only indicator of this problem, so all aspects of the diet and management must be considered. Improving the level of output does not need to come at the expense of the cow’s rumen health. As mentioned above, increasing the amount of fibre in the diet and making gradual changes while maintaining consistency will help maintain an optimal pH. 

Including a proven live yeast culture, such as Yea-Sacc, in your feed can rapidly promote an anaerobic environment, helping increase the presence of desirable, fibre-digesting bacteria and encouraging them to efficiently colonise feed particles. This results in a higher and steadier optimal pH, which can facilitate better performance. Studies have shown that live yeast cultures can lead to an increase in milk solids of 6 per cent.

Yea-Sacc is also proven in grazing systems, as shown in Figure 1, which illustrates the results of a trial carried out on Lyons Estate. The results showed that the pH of the rumen was maintained at 6.0 for significantly longer in the group fed Yea-Sacc than in the control group.  

Figure 2: The relationship between the rumen pH and the percentage of milk fat (Allen, 1997).

Grassland management

The focus of any grassland management programme is to grow and utilise as much grass as possible. Grazing covers of 1,300–1,500kg DM/ha (8-9cm), or what was outlined in the past as ‘the three-leaf stage’ should be the target for the majority of farms. 

The correct graze-out of paddocks in the first round of grazing will result in higher-quality, lush grass growing in the second round. Grazing these covers down to 4-5cm will promote a higher quality of grass further into the year. As outlined above, this will increase the oil content and reduce the fibre content of the grass. While this change promotes good milk and protein yields, it needs to be managed from a butterfat standpoint — and establishing a healthy rumen that can deal with this is key. If supplementation is required — which will be dictated by milk yields and requirements — a good target is to get 16kg of grass DM into the cows. High yields, weather conditions, availability and stocking rates will determine whether extra supplementation or the addition of forage-based buffers are required.

Genetics

Some herds may experience a drop in milk solids every year, despite following every suggestion mentioned above. If this is a persistent problem, genetics should be taken into consideration. 

Some herds that achieve optimal kilogrammes of milk solids throughout the year may find that their percentages are now falling behind, which will affect the bottom line. This could be the result of a genetic issue in the herd. 

As a starting point, look back at the milk record, and compare it with the EBI report on ICBF. This is a long-term solution — but success is ultimately determined by the environment and the genetic potential of the herd. There is no one solution that will fit every farm.