There is considerable variation from genetics and breed type, but the average beef cow produces about 1 1/2 gallons of milk per day during a lactation. Approximately 60-75% of the total milk produced will be in the first 60 days after calving. Studies have shown there is a point of diminishing returns and additional milk production in beef cows is probably wasted because calves will not be able to efficiently utilize large quantities of milk. When we compare this result to the typical dairy cow that may produce 6-10 gallons of milk daily, the divergent nutritional needs are apparent.
The dairy cow has a large outflow of protein, minerals, and water that must be replaced. The beef cow has very little loss of these nutrients from milk production. Data in Table 1. show an 1100-lb. cow eating 22 lbs. of grass hay with 11% crude protein will need to be a pretty exceptional milk producer to require additional protein in the diet. Except for small additions of protein for heavy-milking cows and young cows still growing, the key nutrient is energy. Most beef cows will be able to meet lactation needs with reasonable intake of grass, hay, and stored forages of good quality that will usually supply 1-1.2 Mcal/lb of metabolizable energy.
On a short-term basis, the efficiency of nutrient use for milk production is primarily dependent on the milk production level. As milk yield increases, a lower proportion of total feed intake is used for maintenance (a non-productive requirement that is more or less constant) of the cow. A cow producing 12 kg/d of milk is using about 50% of available nutrients for milk synthesis, whereas the corresponding value is 66% when milk yield increases to 22 kg/d.
Factors Affecting Cow Milk Production
Milk yield of a dairy cow depends on four main factors: (a) genetic ability; (b) feeding program; (c) herd management; and (d) health. As cows continue to improve genetically, we must also improve nutrition and management to allow the cow to produce to her inherited potential. A good dairy feeding program must consider the quantity fed, the suitability of the feed and how and when the feeds are offered. Encouraging a cow to eat large amounts of feed is the key to productive and efficient milk production. Select feeds to ensure maximum intake. All the nutrients the cow requires for milk production (except water) are in the dry material of the feed. High dry matter intake (DMI) results in high nutrient intake and high milk yield.
How Cow Weight Affects Milk Production
A cow weighing 550 kg giving 30 kg milk can eat 3.7% of her body weight in DM daily or about 20.4 kg. A bigger cow (650 kg) at the same milk yield can eat only 3.4% of her weight in DM (22.1 kg per day). Bigger cows at higher milk yield, can eat more feed DM. DMI of cows in early lactation may be reduced by up to 18% below the values in Table 1. Early lactation cows have reduced appetites. Problems such as difficult calving, milk fever, retained afterbirth or twisted stomach will further depress DMI. Most cows increase in DMI gradually after calving and peak in DMI by 10 to 12 weeks of lactation.
Maximum DMI depends on continuous access to fresh, clean, cool water. You should provide water in a well lit area within 15 metres of the feed bunk. Cows drink about 5 litres of water for each kg milk (eg. a cow producing 40 litres of milk will consume 200 litres of water). Cows are thirsty and hungry immediately after milking. Decreasing water intake by 40% results in a 16 to 24% decline in DMI and a large decrease in milk yield. Cows need more water in hot weather. Milking cows can consume 1.8 to 2.2% of body weight daily as DM from average quality dry roughage. Roughage quality is partly determined by fibre levels. Fibre content increases as the forage crop matures. High fibre forage has lower palatability, reduced protein levels, and is less digestible than high quality material. Undigested feed cannot pass out of the rumen. The cow cannot consume more feed until the feed in the rumen is digested. High fibre forages reduce DMI. A cow can eat 3% of body weight as DM from excellent hay but only 1.5% from poor hay
High producing dairy cows will eat 110 to 120 pounds of wet feed a day or 50 to 55 pounds of dry matter (DM) a day. As cows produce more milk, they eat more. A typical diet for a dairy cow could include about 30 to 35 pounds of baled hay (26-30 pounds DM) and 25 pounds of grain mix (22 pounds DM). Grain includes corn, soybean meal, minerals, and vitamins. Bovine milk yield is related to both intrinsic genetic and extrinsic nutritional and environmental factors. Milk composition is related more to genetic factors but is also linked, in part, to extrinsic ones.
This point needs however to be reconsidered in the context of developing countries, especially in the hot and humid tropics. In these countries, several factors limit the use of high-yielding dairy cows:
- highly digestible forages (and fertilizers used to produce them) are not available;
- cereal and other feeds of high nutritive value are not available in excess of what is needed for human or monogastric animal consumption, or are not available at an economic price;
- underfed specialised dairy cows decrease their milk production, but not enough to avoid excessive body weight loss, health and reproduction problems and even mortality;
Milk Production And Calving
Milk yield of dairy cows is clearly greater (25–40 %) when they are suckling their calves twice daily than when machine-milked twice daily. This could be due to a decrease of residual milk and/or to a better response of galactopoietic hormones to suckling. Interestingly, when dairy cows suckle only during the first two months of lactation, they maintain an increased milk yield (above controls) after weaning, suggesting that the number of secreting cells was increased or that there was a carry-over effect on stimulating mechanisms. This can be relevant to simultaneous milking and suckling in dual-purpose herds. milk secretion was increased in the short-term (hours or days) by removal of chemical feedback inhibitor and increased metabolic activity, and in the long-term (months) by increased cell number (resulting either from increased cell proliferation or from decreased cell death rate). The latter is however in contradiction with results in cows previously milked thrice-daily over 20 weeks, in which the increased yield was not maintained when they returned to twice-daily milking. The same observation can also be made after removal of long-term BST treatment
During concurrent pregnancy and lactation, there is a sharp decrease in milk yield during late pregnancy (after about 5 months in the cow), due primarily to increased oestrogen secretion that inhibits milk synthesis (and to some extent to competition for nutrients by the foetus). There is however at the same time a large proliferation of new secretory cells that will produce more milk during the following lactation. This proliferative phase is probably stimulated by drying-off the animals before the next lactation (Mepham, 1983). Hormonal induction of lactation in goats (without pregnancy) leads to lower milk yield and higher persistency, without change in mammary cell metabolic activities