Studies Suggest Mastitis is Not Just a Dairy Issue29 October 2013
Beef producers should look at mastitis like the dairymen do, suggests Cathy Bandyk, a Nutritionist at Quality Liquid Feeds who says that milk production is responsible for over half of pre-weaning calf weight gain variation.
Such a statistic will cost money as each pound of milk produced correlated to in excess of seven pounds of weaning weight, writes Mr Bandyk.
Mastitis infections reduce milk yield, and, in turn, can knock weaning weights 7–12 per cent, or even more, she adds.
Mastitis is, by definition, inflammation of the mammary gland. While these infections can be the result of an injury, virtually all cases are due to infectious agents such as staphylococcus and streptococcus bacteria.
Mastitis is classified by severity into four classes:
•Peracute – swollen, hot, red udder; fever, depression, weight loss, depressed appetite;
•Acute – severe udder inflammation; some fever, mild depression;
•Subacute – less pronounced udder symptoms; cows do not appear sick;
•Subclinical – no visible signs or symptoms, but infectious agents present.
The bacteria responsible for mastitis are widely distributed in the environment. Cows can come in contact with them through bedding, on pastures, in dirt lots, from other cows through cross-suckling by calves, and from flies.
Research has shown that problem bacteria, such as Staphylococcus aureus, can already be present in the teat canals of heifers prior to their first lactation.
Factors often associated with mastitis include wet and muddy conditions, confinement settings, nutritional stress (and resulting impacts on immune function), teats that are wide and flat-tipped, older cows (since pendulous udders are more prone to physical injury and contamination), and significant fly populations.
Biting flies, such as horn flies, can actually drive infectious bacteria into mammary tissue when feeding. Open sores on udders, due to multiple fly bites, are obvious sites for establishment of infections.
And virtually all flies can physically carry disease organisms onto an animal. A common indicator of mastitis is somatic cell count (SCC). White blood cells known as leukocytes constitute the majority of the somatic cells in question. The number of somatic cells increases in response to pathogenic bacteria like S. aureus. Typically, values of less than 100,000 cells/ml would be considered uninfected, while cows with greater than 300,000 cells/ml are infected with significant pathogens.
How Big is the Problem?
Several research projects have evaluated the prevalence and significance of mastitis in beef cows and heifers, reporting infections in 7–54 per cent of the animals involved. In a study at Louisiana State University, mastitis in heifers reduced weaning weights 23 pounds. This matches closely with a couple published veterinary case studies, which reported decreases of 31 ½ and 26 ½ pounds.
Another study (Watts et al.) specifically tied S. aureus infections to a 42-pound depression in pre-weaning gains. In this group of cows, 37 per cent of the animals (and 18 per cent of all quarters) were infected with the organism. Work at North Carolina State evaluated mastitis in a group of Simmental heifers, collecting and analyzing milk samples six times during their initial lactation.
They found mastitis affiliated bacteria in milk from about one third animals. Using a SCC of 292,000 cells/ ml as the dividing line, were grouped into “high” and “low” SCC groups. Elevated SCC levels were associated with a 16 per cent reduction in milk production. At Oklahoma State, scientists working with Hereford and Hereford cross females also showed that mastitis negatively affects the nutritional composition of milk, reducing concentrations of butterfat, lactose, and protein. In this study, they found that 62 per cent of the heifers were infected, and that this value jumped to
to nearly 67 per cent in cows that were nursing their fifth to ninth calf.
Mastitis also impacts reproduction. Israeli research showed that mammary infections can double the length of time it takes a cow to return to heat after calving. This is accompanied by lower levels of reproductive hormones, and reduced follicle function and oocyte competence.
Researchers at Penn State tested the efficacy of an intramammary infusion of cephaprinbenzathine, given at weaning in hopes of reducing mastitis during the following lactation. While this protocol did eliminate existing infections in a majority of animals, it apparently did nothing to prevent new infections. This was somewhat surprising, since this is a proven practice with dairy cows, but the authors suggested the differing response was due to the extended length of the “dry period” in beef vs. dairy production systems.
Regardless, this would probably not be a practical option in most beef cowherds. In another Oklahoma study, intra- muscular injection of antibiotics (oxy-tetracycline) at weaning and/or calving was evaluated as a mitigation tool for mastitis. Unfortunately, the drug was not effective.
Regardless of treatment, 53.7 per cent of cows were infected at weaning, and 43.4 per cent were infected at their subsequent calving date. If one or two quarters were impacted, weaning weights dropped
22 pounds; if three or four quarters were infected, the resulting reduction was 56 pounds.
The predominant bacteria was S. aureus, and its concentration relative to other infectious species increased with cow age. This persistence of S. aureus infections was observed in both Angus and
Brahman sired heifers in research done at the University of Arkansas. Bacterial infection was measured in teat secretions/milk collected during pregnancy and early lactation.
If S. aureus was present in an early sample, it was almost always detected in milk samples taken
later from the same quarter. They also showed that if a quarter was clean during pregnancy, there was a high likelihood it would remain so going into lactation. The authors made a point of commenting on the widespread presence of dry scabs on the udders of these heifers, largely due to horn flies.
All of this highlights the value of mastitis prevention, starting with developing heifers.
Critical control points include:
• Adequate and balanced nutrition to support immune function;
• Good hygiene in facilities and pastures to minimize opportunity for udder contamination and to limit fly breeding sites;
• An integrated fly control program that targets all problem flies. In today’s market, all of these represent cost-effective investments in the health and productivity of the cowherd.