By the time a beef or dairy heifer is about 4–5 months of age, her immune system is close to maturity, says Christopher Chase, DVM, PhD, Dipl. ACVM, South Dakota State University. Amelia Woolums, DVM, PhD, Dipl. ACVIM, Dipl. ACVM, adds, however, that some animals in the first 12–18 months of life may still have an immune system that is relatively naïve if it has not been exposed to important infectious agents during that time. “The immune system may have less memory in a pre-breeding heifer than in an older cow, and it may not be able to respond as quickly or as strongly to challenge,” she says.

It’s important that the young growing heifer is immunized well. Chase says that beginning at 3–4 of months of age in dairy heifers and 4–6 months of age in beef heifers, they should have received a BVDV, IBR and Lepto hardjo and then receive a booster vaccination two to three months following the initial dose. Woolums adds that depending on herd management and geography, vaccinations could also include Trichomonas foetus or Brucella vaccines. Vaccination of dairy heifers with a J-5 bacterin may be part of heifer development plans, too. 

“I think over-vaccinating young calves can have adverse effects,” Chase says. “Those protocols that give multiple vaccinations particularly to animals under 3 months of age can be detrimental.”

Vaccinations prior to breeding

Pre-breeding vaccinations should help prime an immune response in order to ensure heifers develop colostral antibody levels that will help protect their calves throughout their reproductive life.

As far as pre-breeding vaccines that are intended to help ensure reproductive efficiency by preventing infections that can affect pregnancy, the heifer must have time to develop a protective immune response before she is bred. Chase says the first dose in a naïve animal should be given at least two months prior to breeding. In animals previously vaccinated, they should be vaccinated preferably a month before breeding with two weeks being the minimum.

Vaccines can sometimes induce a significant inflammatory response that could be detrimental to conception and maintenance of pregnancy, thus it is not advisable to vaccinate near the time of breeding, Woolums explains. “The inflammatory response can be due to live organisms in modified-live vaccine, or to adjuvants that can be present in both modified-live and inactivated vaccines,” she says. “Vaccines against Gram-negative bacteria and clostridial vaccines can also induce significant inflammatory reactions due to components of the bacteria included in the vaccines”.

Chase adds that the IBR component of vaccines can have a negative impact and cause necrosis of the corpus luteum, so it’s not advisable to vaccinate too close to breeding. This is not as critical in animals that have received IBR vaccinations prior to  a booster dose given prior to breeding.

Stress and nutrition

Prolonged or ongoing stress can have a negative impact on immunity, so management practices that lead to chronic stress through factors such as crowding, excessively hot or cold environmental temperatures, and mixing of unfamiliar animals could impact the immune response in developing heifers.

The trace minerals — copper, selenium and zinc — are very important along with vitamin E for the pre-breeding heifer’s immune system. “They are what I consider the ‘immune minerals’ and deficiencies can result in failure of immunization,” explains Chase. “Since the development of the immune system and the immune response require adequate energy and protein, poor nutritional management can affect any immune response.”

Supplementation of nutrients in excess of required levels has not been reliably found to improve immune responsiveness, Woolums states. Some though not all studies have found an immunological benefit to supplementing animals with B vitamins around the time of shipment, which may be relevant in some heifer management situations. 

Chase adds that poor nutrition during this pre-breeding growing period can derail the immune system and “you cannot catch up” once you get behind in this period.