Feeding dry cows - down but not out Jon Moorby and Richard Dewhurst Growth 54 Replenishing fat reserves 55 Replenishing protein reserves and preparing for lactation 56 Rumen development and feed intake potential 56
Jon Moorby and Richard Dewhurst Dairy cows produce most milk in the first few months after producing a calf and so farmers try to get their cows to calve roughly once a year in order to maximise average yields. Farmers stop milking cows for a period of 6-8 weeks before each calving to give cows an opportunity to replenish their reserves ready for the demands of the next lactation. This period is called the dry period ; the name dry cow reinforces the view of farmers that these animals are in a non-productive state and they often presume that this period is unimportant. However, work at IGER and elsewhere has shown that the dry period is a period of intense metabolic activity and adaptation, and that feeding at this time has important consequences for the subsequent lactation. The management of body reserves is crucial to maximise the utilisation of forage and to minimise health problems of cows on high-forage systems. Milk protein concentration response (% of control) 1 5 95 9 9 95 5 Feed intake response (% of control) Figure 9.1 Special diets provided to cows during the dry period (in comparison with control cows fed standard diets) led to a range of feed intakes after calving which were directly related to milk protein levels. We became interested in dry period nutrition because of evidence that it could lead to a low milk protein syndrome in the subsequent lactation. This syndrome typically involves the development of low milk-protein levels, which is particularly noticeable with autumn-calving cows in mid to late winter and is difficult to rectify by short-term changes in feeding. The level of protein in milk is important because it determines the yield of cheese that dairies can produce from the milk. In general terms, nutrition shortly before calving can have dramatic effects on feed intake, and consequently on milk protein content, during the early part of the next lactation (Figure 9.1). More recently, we have become interested in the health and welfare implications of dry cow nutrition, particularly through effects on feed intake in early lactation. Many health and welfare problems occur around calving, and many are related to feeding in this period. We have progressively realised that these effects are linked by a common theme of low feed intakes and loss of body reserves in early lactation. Growth The dry period represents an important opportunity for younger animals to complete their growth. The conflicting demands of the naturally persistent heifer lactation, the requirements of the developing calf, and the need to grow, present pregnant heifers with conflicts which are difficult to resolve. In one study with both 2- and 3-year old calving heifers, we showed that underfeeding 54
Milk yield (kg/d) 35 25 15 3 ow 3 High 2 ow 2 High 2 4 6 8 12 14 16 18 22 Week of actation Figure 9.2 Effect of age of first calving (2- or 3-years old) and level of concentrate feeding in the second part of the first lactation (2 or 7 kg/day concentrates) on milk yields (kg/day) in the second lactation. All animals were offered the same diet (fixed allocation of concentrates and ad libitum access to grass silage) in the second lactation. 2-year old heifers during the end of their first lactation can have detrimental effects on second lactation performance (Figure 9.2). In this experiment we offered two levels of concentrates (2 or 7 kg/d) during the first lactation from confirmation of pregnancy to drying off. We found that younger animals given the lower level Gene-mixing by natural of dispersal concentrate along did tracks not milk as well in their second lactation, but that there was no effect on the older animals. It is clearly important to feed animals a good diet during the dry period in order to compensate for a previously limited diet. Eye muscle Replenishing fat reserves We have used a number of techniques to assess the body fat and protein stores of cows including the use of ultrasound imaging (Figure 9.3) and a body condition score (CS). Body CS is assessed by feeling the fat cover at sites on the loin and around the tail head, and ranges from 1 (emaciated) to 5 (obese). Most cows are in the CS range 1.5 to 4.. Dry cows can easily gain fat in a relatively short space of time because they are used to eating large amounts when lactating. However, the old practice of steaming up (giving lots of concentrates before calving) often led to cows getting too fat, which leads to low intakes and deleterious live-weight loss in early lactation. Current opinion suggests that the growth rate of well-conditioned cows (CS 2.5-3) during the dry period should not greatly exceed the growth rate of the conceptus (calf and placenta) of around.6 kg/day, and that the diet should be adjusted accordingly. N balance (g/day) 4 - - Vertebra - -4 6 to 7 14 to 15 21 to 22 weeks of lactation Figure 9.4 Nitrogen gain or loss (g/day) in cows at three stages of lactation, showing utilisation of body N reserves in early lactation and replenishment of reserves in mid-lactation. Figure 9.3 Real-time ultrasound image of the loin region of a cow showing the region at which back muscle depth (yellow arrow) is measured in our studies. 55
N balance (g/d) 6 5 4 Straw mix ow Protein Silage Only Medium Protein Silage + PM High Protein Figure 9.5 Nitrogen balance of dry cows given a range of diets varying in N content. Cows gaining less than about g/day nitrogen must have been mobilising maternal N in order to sustain the deposition of N in the conceptus at this stage of gestation (PM= high protein maize gluten meal). Replenishing protein reserves and preparing for lactation Cows will utilise body N (protein) in early lactation and replace it later (Figure 9.4) despite the fact that there are important protein-requiring processes going on in a range of tissues. However, if cows are given a poor dry period diet, they can also use body protein before calving (Figure 9.5) to support the needs of the developing foetal calf which has a high requirement for amino acids; it uses them both as the building blocks of protein and, inefficiently, as energy. The development of the mammary gland, gut and liver also contribute to the rapid growth in protein requirements in the late dry period and early lactation. Over and above their requirements for maintenance and calf growth, we have shown that cows will incorporate additional nitrogen in their bodies when given diets that have a high protein content. We conclude that although body protein reserves change in response to feeding (or underfeeding), they probably don t directly cause differences in milk production and composition. However, it is probably important that body protein is available to allow cows to reach their milking potential in early lactation. Rumen development and feed intake potential The strong correlation between forage intakes before and after calving has been a growing interest in our studies as this is another way in which dry period feeding can affect the next lactation. Figure 9.6 shows that the low feed intakes of cows given a mixture of grass silage and barley straw in the dry period persisted for about one month after calving. This is an important effect because the first month of lactation is a period when cows are short of energy and protein and need to eat as much as possible in order to avoid excessive weight loss and health problems. We are interested in possible mechanisms by which feed intake in the dry period can affect intake during early lactation, including effects on hormones, metabolites, rumen processes, meal patterns and rumination activity. The late dry Forage DM intake (kg/day) 12 11 9 8 7 6 5 Silage only Straw mix Silage + PM 4-5 5 15 25 Week of actation Figure 9.6 Forage DM intake (kg/day) of cows offered one of 3 different diets during the dry period and a standard diet after calving. Note the residual low intakes of cows offered the silage/straw mixture in the dry period. 56
Forage DM intake (kg/d) 12 8 6 4 2 Figure 9.7 Forage DM intake (kg/day) of cows offered one of 4 diets in the dry period. Note the increased intake when maize high protein (PM) gluten meal was supplemented alongside the protein-deficient silage/straw mixture. period and early weeks of lactation involve large changes in the diet of dairy cows, and workers have proposed rumen stretching, and papillae conditioning or microbe conditioning mechanisms to explain effects of dry period feeding on lactation performance. It has been suggested that feeding straw to dry cows may improve lactation performance by rumen stretching or increasing the capacity of the rumen for forage. However, as the preceding section outlines, we have only found negative effects of including straw in the dry cow diet and no evidence for beneficial effects of rumen stretching. We suggest that it is more important for cows to be accustomed to a high throughput of good forage in the late dry period. Protein supplements, such as high protein maize gluten meal, can boost total feed intake and may increase forage intake of dry cows if the rumen is short of Grass silage Grass silage + PM Silage/straw mix Silage/straw mix + PM -5-4 -3-2 -1 Weeks before calving protein (rumen degradable protein), such as occurs when a lot of straw (which has a low protein content) is included in the diet (Figure 9.7). Small amounts of barley/concentrates may promote forage intake, although we have seen no residual benefit on performance after calving. The financial support of the Ministry of Agriculture, Fisheries and Food, as well as the Milk Development Council for the Dry Cow Programme at IGER is acknowledged. Contact: jon.moorby or richard.dewhurst (@bbsrc.ac.uk) 57