Introduction
Transitioning a heifer calf into a productive, long-term member of the breeding herd requires attention to many important factors, including nutrition, genetic and breeding decisions, and environmental management. Disease and health challenges, however, can undermine all that work. Health issues can derail a heifer’s progress at every stage – from her own development to reproductive success, calving, and rebreeding.
The Heifer’s Ability to Stay Healthy
Disease problems, even early in life, can have lifelong effects on the breeding female. The most common of these, Bovine Respiratory Disease Complex (BRDC), might not seem like it has much to do with reproduction. However, evidence from the dairy world shows that heifers affected by BRDC as calves exhibit decreased survival to first calving, poorer calving scores, lower first lactation milk production, and a higher chance of leaving the herd after first calving due to the disease’s draining effect on immunity and other body systems.
Preventing BRDC needs to start well before the heifer is selected as a replacement. Vaccination for pathogens such as Infectious Bovine Rhinotracheitis (IBR, or “red nose”), Bovine Respiratory Syncytial Virus, Mannheimia hemolytica and Histophilus somni, should begin before weaning or earlier, with boosters as required by the vaccine. Close regular monitoring for illness and prompt treatment is important for every calf, but especially for potential replacement heifers. Paying attention to biosecurity concepts, particularly segregating feeder calves or other animals brought into the herd, will help prevent herd BRDC problems as well.
Examples of other diseases affecting heifer health include pinkeye and footrot. These conditions result in lower weight gains, poorer body condition scores, increased stress, and decreased mobility, all potentially detrimental to future fertility. Managing environmental factors such as flies and other eye irritants, and muddy lots are important, while pinkeye vaccination should be considered for heifers. For these diseases, prompt detection and treatment are critical to minimize their effects.
Internal and external parasites are also detrimental to overall heifer health and productivity; calves coming off pasture should be dewormed with an effective parasiticide.
The Heifer’s Ability to Become – and Stay – Pregnant
A heifer’s capacity to become – and stay – pregnant hinges on nutritional, hormonal, genetic, and immunologic factors all working together optimally. Lurking in the background, however, is the threat of infectious reproductive diseases. Of these infections, those caused by IBR and Bovine Viral Diarrhea Virus (BVDV) are especially important. Both can cause infertility and pregnancy loss; BVDV infections during pregnancy can result in calves born with birth defects or persistent BVDV infections. With their relatively inexperienced immune systems, heifers are at increased risk for these problems.
Fortunately, effective vaccines are available to protect heifers and their pregnancies against these viruses. Recent research can help inform decisions about the version of and the timing of these vaccines. This information reinforces the importance of setting heifers up as calves and before their first breeding with modified live (MLV) versions of these vaccines (which conveniently meshes with BRDC prevention mentioned above). In general, pre-breeding vaccines should be given well ahead of breeding or synchronization as to not interfere with the estrus cycle, and killed vaccines should be considered prior to subsequent breeding seasons. Biosecurity is another important aspect of BVDV prevention – in particular, testing incoming herd animals for BVDV persistent infections.
Leptospirosis infections can adversely impact fertility and pregnancy success. Two categories of this bacteria affect cattle: “lepto” strains picked up from environmental sources causing sporadic pregnancy loss, and cattle-adapted strains that can persist in kidneys and reproductive tracts and spread through a herd, causing longer-term insidious reproductive difficulties. Vaccines for both of these versions exist and should be given to replacement heifers earlier than pre-breeding if possible, as heifers can contract and harbor these germs even prior to their selection as replacements.
Neospora infections can affect heifer pregnancies more profoundly than those of older cows. Heifers that blood test positive for Neospora exhibit higher open rates compared to those that are negative. Because no vaccines exist for neosporosis, blood testing heifers prior to their selection as replacements is a worthy strategy.
The Heifer’s Ability to Raise a Healthy Calf
Calves born to heifers are a well-known “population at risk” when it comes to health challenges. Much of that risk is related to colostrum quantity and quality. Optimal heifer nutrition can improve both. Heifers with lower body condition scores produce less colostrum with lower antibody concentration. Therefore, maintaining heifers in moderate to good body condition at calving will optimize colostrum production, as well as future milk production their ability to rebreed (see below).
Pre-calving vaccination can improve heifer colostrum quality. Common “scours” vaccine programs utilize vaccines containing diarrhea-causing strains of E. coli, Clostridium perfringens, rotavirus and coronavirus. These killed vaccines require boosters when given to heifers, so timing of the first dose becomes important. Because antibodies from the heifer’s bloodstream begin moving into colostrum five weeks before calving, the second dose of vaccine should be given around that time. This requires the initial dose to be given several weeks before that (follow label directions). These vaccines do not elevate the overall antibody concentration in colostrum, but they do increase the level of antibodies against those pathogens.
The Heifer’s Ability to Breed Back
First calf heifers are notorious for their difficulty in becoming pregnant during their second breeding season. Most of that phenomenon relates to body condition score when breeding commences, but other factors contribute as well. The increased risk of dystocia that heifers experience can lead to uterine infections and retained placentas, both of which delay breedback. Prompt recognition and treatment – with veterinary advice -- can help minimize the negative impact of these conditions. Other, non-reproductive related conditions can also hasten a heifer’s early removal from the breeding herd, including mastitis, pinkeye, and footrot – all of which should be quickly identified and treated, again with guidance from a veterinarian.
Managing reproductive vaccine choice and timing is also important as heifers approach their second breeding season (see discussion above). In general, killed vaccines given well ahead of the breeding season represent less risk to a successful early breeding compared to live vaccines given close to the onset of estrus.
Summary
The length and success of a heifer’s breeding career depends on preventing and managing their health challenges – starting well before they’re even identified as breeding herd candidates. At every step along the way, advice from a veterinarian with knowledge of your herd can help you avoid many of these health pitfalls.
