By Trey Gafnea
Introduction
Milk production in beef cows is the most important factor affecting calf pre-weaning growth and subsequent body weight at weaning. In fact, each additional lb of milk produced per day may increase calf pre-weaning weight 15 to 30 lb. Thus, factors that limit milk production in the dam will detrimentally affect weaning weight of the calf. Bovine mastitis, a disease of the mammary gland that significantly reduces milk production in dairy, also occurs in beef cows.
The prevalence of mastitis in beef dams ranges between 7 and 54%, and is associated with costly reductions in calf weaning weight. Most studies investigating mastitis prevalence in beef animals have concentrated on older, mature cows. The purpose of the study reported here was to determine the prevalence of mastitis in first-calf beef heifers and evaluate the influence of mastitis in dams on weaning weights of their calves.
Materials and Methods
This study evaluated 30 crossbred beef heifers of ¼ to ½ Brahman inheritance for presence of mastitis. At the initial sampling taken in mid-gestation, quarter milk samples were obtained from each udder and processed for microbiological examination to determine presence or absence of mastitis and the types of bacteria causing the disease. Subsequent samplings for mastitis and SCC were conducted prepartum, early lactation, mid-lactation, weaning, and mid-gestation with their second calves.
Results and Discussion
Bacteriological examination of quarter milk samples demonstrated that the most commonly isolated mastitis-causing organisms were the coagulase-negative staphylococci also known as CNS (10.9%) followed by Staph. aureus (6.6%), which are normal inhabitants of teat skin and shown to be transmitted by flies; very few environmental streptococci (1%) or coliforms (0.1%) were found. Culturing of swabs collected from scabs found on teat surfaces revealed Staph. aureus. Biting flies contribute to the formation and infection of such scabs, and serve as vectors for the transmission of mastitis-causing bacteria, such as Staph. aureus, among cows.
Over the 6 sampling periods, SCC averaged 436,000/ml from uninfected quarters, whereas SCC from infected quarters averaged 3,539, 000/ml. The highest SCC (6,000,000/ml) were found in quarters infected with Staph. aureus, which indicate chronic inflammation and damage to the developing udder tissues of beef heifers.
Most infections were found in the front quarters: 25 and 27% of the right front and left front quarters were infected, whereas only 8% of left rear and 15% of right rear quarters were infected. High prevalence in front quarters might be a function of location with respect to the tail. This speculation is supported by the observation that the front quarters are less accessible than rear quarters to the tail switch, which helps to repel biting flies, which are instrumental in the initiation of mastitis. In addition, the front quarters are more accessible to the calf for nursing, and because they are suckled more frequently, the transmission of mastitis-causing bacteria from the calf’s mouth to front teats may occur at a greater frequency than rear teats.
Frequency of mastitis over the 6 sampling periods from mid-gestation of the first pregnancy through mid-gestation of the second pregnancy is shown in Figure 1. The percentage of quarters infected decreased slightly from a high of 30% during mid-gestation of the first pregnancy to 25% during the prepartum period, and then to a low of 10% in early lactation. Prevalence of infection gradually increased through mid-lactation and weaning, and returned to 30% during mid-gestation of the second pregnancy.
At the time of weaning, the adjusted 205-day (d) calf weight ranged from 391 to 602 lb. Dams across breed type were grouped according to having weaned low (391 to 450 lb) or high (451 to 602 lb) 205-d weight calves. Overall prevalence of mastitis among cows weaning low-weight calves was almost 19% of quarters, while that among cows weaning high-weight calves was only 11.1%. Likewise, prevalences of CNS and Staph. aureus infections were higher among heifers of low-weight calves (Figure 2). Angus- and Brangus-sired heifers exhibited a higher level of infection (35 and 38%, respectively) than Gelbvieh- (8%) and Gelbray-sired (5%) heifers.
Overall, the mean 205-d weaning weight of calves from dams having at least one mastitic quarter (453 lb) was 18 lb less than that of calves weaned from dams having no history of mastitis (471 lb). Staph. aureus is a more pathogenic microorganism than CNS, eliciting very high SCC in milk and is detrimental to milk-producing tissues of the udder, and as a result, the mean weaning weight of calves from dams with Staph. aureus mastitis (448 lb) was significantly lower (23 lb less) than that of calves from uninfected dams (471 lb) (Figure 3); the weaning weight of calves from dams infected with CNS (456 lb) was also significantly lower (-15 lb).
Conclusions
As observed in multiparous beef cows, mastitis is quite prevalent in first calf beef heifers and can lead to a reduction in weaning weight of up to 23 lb.
At a current market price of $2.50 per lb for 400- to 500-lb beef calves, producers may be losing $50-$60 per head or approximately 5% of calf sale value due to the presence of mastitis in their dams, which reduces milk production and milk quality. A mastitis management program developed for dairy heifers has shown that administration of nonlactating cow antibiotic infusion products, vaccination, and fly control reduced the level of mastitis when heifers freshen, and resulted in increased milk yield during the first lactation. Similar programs for bred beef heifers could be instrumental in reducing the level of udder infection in beef heifers and cows, thereby increasing milk yield and maximizing subsequent calf weaning weight.
Source:uga.edu