04/12/2022
The productivity of an individual cow is the sum of the value of the milk she produces, the value of her offspring, and her individual market value when she leaves the herd. Many factors influence individual cow productivity, which is also based on longevity and the proportion of the cow’s lifetime spent producing milk. Nonproductive periods include the period from birth until first parturition and dry periods before subsequent calvings. Heifers must be managed to reach appropriate breeding size by 13–15 months of age to maximize lifetime production.
Milk yield is related to stage of lactation. Milk yield increases rapidly after calving, reaches a plateau 40–60 days after calving, and then declines at a rate of 5%–10%/month. The rate of decline is lower in first-parity animals than in older cows. Good reproductive management ensures that the largest proportion of a cow’s total lifetime production is spent during early high-producing stages of lactation rather than late, lower-producing periods. Milk yield increases with age and parity until about the sixth lactation; these cows may produce up to 25% more milk volume than first lactation cows. Health disorders or other management problems that reduce longevity have a negative impact on productivity.
Nutritional Management
In most dairy herds, nutritional management is the most important determinant of herd productivity. The relationship between nutrition and productivity begins at birth. The feeding system must deliver the necessary nutrients to each cow at the correct stage of growth and lactation to maintain optimal productivity.
Research has documented the importance of the ration fed to cows in the transition during the 2–3 weeks before calving. Dry cows are fed a diet relatively low in carbohydrates and protein and high in fiber, reflecting the low nutrient demands of the nonlactating cow. The transition period ration must allow the rumen to adapt to the lower-forage, more nutrient-dense lactating ration. Further, the stresses associated with moving animals to the transition pen and of calving itself tend to reduce feed consumption at this critical time. Reduced feed intake in the transition period is associated with excessive weight loss; reduced peak milk production; and an increased incidence of postpartum diseases such as metritis, retained placenta, ketosis, displaced abomasum, and fatty liver. Research has documented the benefits of monitoring postpartum cattle for excessive energy mobilization by measuring blood levels of beta-hydroxybutyric acid, one of the ketone bodies.
Rations for lactating cows must strike a balance between providing high levels of energy and protein to support high milk production and maintaining optimal rumen health and motility. Subacute ruminal acidosis (SARA) is a common condition resulting from excessive fermentable carbohydrates, inadequate fiber of adequate length, or a combination of the two. Health effects of SARA include digestive upsets and diarrhea, reduced feed consumption and milk production, reduced butterfat content of milk, ulceration of rumen epithelium, liver abscessation, and a series of foot problems related to subclinical laminitis.
The choice of a feeding system is associated with herd size and production level. Three general types of feeding systems are used currently by dairy farmers: total mixed ration (TMR), component feeding, and management-intensive grazing. Each of these systems, when implemented correctly, can deliver adequate nutrients for a highly productive dairy herd. Each system has its own inherent challenges in achieving optimal productivity.
The use of TMR feeding systems has increased as more herds have adopted free-stall or dry-lot housing. TMR diets have several advantages: cows consume the desired proportion of forages, risk of digestive upset is reduced, feed efficiency is increased, byproduct feeds may be used, accuracy of diet formulation is higher, and labor needs are reduced.
However, the performance of herds using TMR diets can be adversely affected by errors in ration formulation and feed delivery. An oft-quoted statement illustrates the challenges of TMR feeding. There are 3 rations for a dairy herd: the ration on paper as formulated by the nutritionist, the ration delivered to the cows, and the ration the cows actually consume.
Some common formulation or delivery errors include:
inadequate or nonexistent forage testing
variation in forage dry matter
variation in dry-matter intakes
overmixing of diets that reduces effective fiber length
errors or imprecision in the mixing of the ration
overfeeding or underfeeding energy to late-lactation cattle
When TMR diets are fed, feeding mistakes are often spread across the entire group or herd. Health management programs of herds that receive TMR diets should include systems to monitor the adequacy of the ration formulation and delivery.
Component-fed herds receive grain and forage separately. Advocates of component feeding emphasize the ability to meet the production and metabolic needs of individual cows throughout their production cycle. The primary disadvantage of component feeding systems is that the cow receives concentrates separate from forages, enabling ingestion of these concentrates in a single feeding, leading to rumen acidosis and indigestion.
Management-intensive grazing systems can be used to meet the needs of modern dairy cows. In some regions of the world (eg, New Zealand and Australia), pasture-based systems are the predominant method of feeding dairy cattle. In these truly pastoral systems, nutrition frequently limits productivity because of significant annual variation in growing conditions. However, the economic model in such a system emphasizes low costs of production rather than maximal productivity. In other areas, such as Britain and the northeastern USA, rotational grazing is used to provide for the forage requirements of lactating cattle during the spring and summer months, and supplemental concentrates and corn silage are fed to achieve high milk production. In both situations, seasonal calving is practiced to match rainy or spring season pasture conditions with the energy needs of early lactation cows. Attention to reproductive management is therefore critical for herds in which there is an attempt to breed all cows within a defined period.
Production management programs for herds using management-intensive grazing systems must include programs to control bloat, hypomagnesemia, and copper and selenium deficiency. Pastured cattle may walk considerable distances to harvest forages. Therefore, a system to monitor and minimize lameness must be included in the health delivery system.
Reproductive Management
Artificial insemination (AI) using semen from genetically superior sires is the most important factor leading to increased productivity in the dairy industry, accounting for at least 150 kg increased annual production since its inception. Even today, the genetic potential for milk production greatly exceeds the actual milk yield achieved on most farms. Reproductive disorders are the most common and costly reasons for premature culling of dairy cows.
In conventional dairy herds in which calving occurs throughout the year, suboptimal reproductive management leads to the failure of cows to conceive in a timely fashion, or at all. Cows remaining nonpregnant (open) reduce productivity in the following ways:
Open cows spend more time in late lactation, with lower milk production
Cows taking longer to conceive may dry off sooner, leading to longer dry periods
Risk of culling increases greatly in cows remaining open >300 days after calving
Fewer replacement heifers are available
Higher labor and treatment costs are associated with prolonged efforts to synchronize and breed open cows
Successful AI requires that cows be inseminated during estrus in a narrow range of optimal fertility, and that the semen be thawed properly, transported quickly to the cow, and deposited in the appropriate area of the reproductive tract.
The most important factor affecting the success of an AI program is the detection of estrus: US data indicate that < 40% of estrus periods were detected in lactating dairy cattle. Efforts to improve heat detection using estrus synchronization and artificial detection aids have been largely unsuccessful and are hampered by the reduced duration and intensity of estrus exhibited by modern US Holsteins, and by the greater difficulty in observing estrus on larger farms.
Because estrus detection rates are so low, some dairy managers have returned to extensive use of natural service sires to ensure that cows conceive promptly. In these herds, breeding soundness examinations and bull management programs should be part of routine management practices to ensure continued herd productivity. However, the problems associated with natural service include reduced genetic improvement of offspring; costs associated with purchase, raising, and feeding bulls; damage to facilities; and danger to people.
Researchers in Wisconsin and Florida have developed hormonal synchronization protocols that allow timed insemination to be performed with acceptable conception rates. These programs have been widely adopted and have enabled herds to dramatically increase the number of pregnant cows throughout defined time periods. Many of the injections and the inseminations can be scheduled on a weekly basis, leading to more efficient use of labor. These timed insemination programs have led to a resurgence in the use of AI and are significantly increasing the genetic milk production potential of the dairy cow.
The widespread adoption of aggressive, timed insemination programs has emphasized the importance of early and accurate pregnancy diagnosis. Cattle found to be nonpregnant (open) at 30–35 days after breeding can be resynchronized immediately to minimize the time they remain open. Accuracy is essential, because a pregnant cow mistakenly called open will be given prostaglandin F2alpha as part of the synchronization program and will abort the embryo. Veterinarians are increasingly adopting transrectal ultrasonography for routine pregnancy diagnosis, because pregnancy diagnosis at 32 days using ultrasound is simple, reliable, and safe.
Another option for early pregnancy diagnosis in cattle is the use of blood tests to identify the presence of pregnancy-associated glycoproteins. These tests are inexpensive and are highly specific and sensitive. In herds whose veterinarians cannot visit frequently enough, herd managers can collect blood samples from cows bred 30 days or more and ship them to laboratories performing the tests. Because there is an expected 5%–10% embryonic loss between 32 and 60 days after conception, early pregnancy detection by any method should be followed by manual confirmation after day 60 of gestation.
