Management to increase milk protein

Many changes take place during the production cycle of a dairy cow. A clear understanding of the major changes will help identify some of the key stages where milk protein content can be influenced. The typical pattern of changes in feed intake, milk yield and bodyweight through the production cycle is shown in Figure 1.

Figure 1. Changes in feed intake, milk yield and liveweight for a mature dairy cow

Milk protein content is affected by many management factors. Some management practices can be changed in the short term, others require long term commitments. Cows reach peak yield before they achieve their maximum dry matter intakes. The dry matter intake in early lactation is insufficient to meet energy demands, resulting in an energy deficit and bodyweight loss.

Assessment of the level of fat cover on dairy cows is a useful parameter by which to determine their nutritional status. Scoring involves a 'hands-on' assessment of the cow to determine the fat cover over certain areas ie. the short ribs/loin and tail area. The purpose is to monitor any changes in bodyweight and mobilisation of body tissue and therefore, to be able to address energy intake problems before they affect the cow’s condition, milk protein content, milk yield and ultimately profitability.

The level of fat cover is assessed on a numerical score from 0 (very thin) to 5 (very fat). It is important that measurements are as consistent as possible ie. the same person assessing on each occasion. At Greenmount, cows are conditioned scored on a monthly basis with the aim of monitoring the critical points in the production cycle where target condition scores should be achieved - at drying off, calving and 8-10 weeks after calving.

cow 325 - condition score 2

cow 318 - condition score 3

Cows should be managed in early lactation to reach peak dry matter intake as early as possible. Excessive weight loss after calving will lead to reduced milk protein content, as well as reduced milk yield, fertility and overall health.

Spring calving herds have traditionally a higher milk protein content than those calved in the autumn. Seasonally low milk production from the autumn calving cow normally results from the combination of stage of lactation effects and declining nutritional status over the winter. Calving cows in the spring allows the cows energy requirements to be closely matched to the supply of spring grass. Turnout to grass comes early enough in the lactation to maintain protein levels above those of autumn calvers.

Heifers have higher milk protein in their first lactation, with a decline of 0.05% between the first and fourth lactation. Maintaining a young herd by implementing an economic replacement rate will improve milk protein. Also, if a strategic breeding programme is in place to raise milk protein a replacement rate of 20-25% will enhance the rate of genetic progress in all profitability traits.

Dairy cows do not reach their mature size until their second or third lactations. Younger animals eg. heifers in their first lactation, not only need to be fed for the milk they produce, but also for growth - up to 150 KG liveweight. First lactation heifers will benefit considerably from being kept in a separate group during the housing period. Separate grouping reduces bullying from dominant cows in the herd and hence reduces stress.

Separate grouping of heifers enables these animals to be fed and managed differently to maximise dry matter intakes and help them achieve their full potential as well as improving milk protein content. Heifers at Greenmount have been maintained as a separate group for a number of years. This is a key aspect of the management of the College herd. Excellent silage intakes have been achieved by heifers under this regime, see Figure 2

Figure 2. Silage dry matter intakes of cows and first lactation heifers at Greenmount.

The protein content of milk produced is an excellent guide to the overall health and nutritional status of the herd. If milk protein content is good then few major problems exist with feeding and management. Cows which are back in calf tend to produce higher milk protein and so herd fertility can benefit milk protein.

Lameness and mastitis are major sources of economic loss to the dairy herd. Lame cows spend less time eating and therefore their energy intake and milk protein level will be reduced. Milk protein level is reduced during a case of clinical mastitis and in cows with persistently high cell counts. The effect of internal parasites such as worms and fluke is also to lower the protein content of milk.

Dry cow therapy is routine at Greenmount

The dry period provides an ideal opportunity to treat mastitis and parasite problems by administering anthelmintic drenches and dry cow tubes without the need to discard milk. At drying off, antibiotic therapy is given to all cows at Greenmount as well as other routine treatments such as foot trimming, vaccinations and a fluke dose.

The dry period is a critical time in the management of the modern dairy cow. It is essential that the cow is properly prepared for the subsequent lactation. During this period the cow will rebuild mammary tissue and replenish body reserves prior to calving.

Figure 3: Effect of condition score at calving on subsequent dry matter intake

source: AFRC

A marked contrast in dry matter intakes post calving is evident between cows in different body condition scores, see Figure 3. Cows in fit condition have higher intakes and make less use of body fat reserves than cows in excess condition. This will have beneficial effects in milk protein production.

Dry cow management is a key component in protein improvement

Ideally the cow should be managed to dry off in the condition in which she is expected to calve down, i.e. 3. Work at Hillsborough has shown that cows which are too fat or too thin at calving produce lower milk protein (up to 0.15% less) than those in fit condition.

At Greenmount the target drying off condition score is 2.5 - 3.0 at least six weeks before calving. Heifers at the end of their first lactation are dried off eight weeks prior to calving and any animal which is below condition score 2.5 is dried off two weeks earlier than normal to allow more time for body reserves to be replenished. All cows receive a specialist dry cow mineral either sprinkled on the silage or as part of a pre calver concentrate. Cows in ideal body condition are maintained on fibrous silage or tightly stocked at grass whilst those below target are offered higher quality forage.

Dry cows - maintaining body condition on fibrous silage and straw

Pre-calver feeding of dry cows during the last month before calving is a routine that has been adopted at Greenmount. Pre-calver feeds are recommended to supply 250-300g digestible undegradable protein (DUP) per day. Sources of DUP include protected soya or praire meal. The ration should be balanced to ensure that energy intake remains at approximately 90 to 100 MJ/ ME/day.

Although variable results have been produced on the response in milk protein to pre-calver feeding, best results seem to have been achieved with higher yielding animals, those with persistent lactations, those on poor quality diets and animals starting their second lactation.

In the last two to three weeks of pregnancy dry matter intakes can fall by 25 percent. The energy requirement at this time is approximately 100 MJ but rises after calving to over 200 MJ in early lactation. It is therefore essential to condition the rumen for high intake potential prior to the start of the next lactation.

Minimise nutritional stress during the transition period

During the housing period cows at Greenmount are moved to a straw-bedded court seven to ten days before calving. Once in this pen the cows are fed the same silage as the milking herd and are also offered small quantities (one to two kilograms) of the lactation concentrate during this period. The aim of this practice is to minimise nutritional stress by allowing a gradual transition onto the lactating diet and to achieve peak feed intake as early as possible during the lactation. This minimises body condition loss and improves milk protein.

To improve milk protein through management: