Effects of natural intramammary Corynebacterium bovis infection on milk yield and composition.

The objective was to assess effect of Corynebacterium bovis infection of the bovine mammary gland on milk yield and composition. Yield and composition of milk from 53 Corynebacterium bovis-infected quarters of 44 cows at four consecutive milkings were compared with those of the contralateral uninfected quarters. Differences between infected and uninfected quarters in milk, fat, and protein yield and in fat and protein content were small and statistically nonsignificant. Numbers of somatic cells were moderately but significantly higher (119,000 vs. 79,000 cells/ml) in infected than in uninfected quarters.

Effect of automatic backflushing on number of new intramammary infections, bacteria on teatcup liners, and milk iodine.

Effect of an automatic iodine (15 ppm) backflushing system on incidence of new intramammary infections, teatcup liner bacterial populations, and milk iodine was tested in a herd free of Streptococcus agalactiae and with a low prevalence of Staphylococcus aureus. In an 11-mo trial, backflushing was applied to teatcups that milked the right half of the udder; the left half served as control. Clawpieces were divided into left and right halves with each having a milk outlet. Postmilking teat dipping was discontinued. All lactating cows in the University herd were used, averaging 154 with normal attrition and additions of new individuals as they calved. Backflushing reduced numbers of staphylococci recovered from liners by 98.5% and Gram-negative bacteria by 99.5% as compared with unflushed liners. Backflushing significantly reduced new infections caused by Corynebacterium bovis. However, there was no effect on incidence of new infections by staphylococci, streptococci, or coliforms. Iodine concentrations averaged 243 micrograms per liter in milk from control quarters and 486 micrograms from backflushed udder halves. Interior surface cracking was more severe in backflushed teatcup liners than in control liners. These results do not justify the use of backflushing in a herd with low prevalence of contagious pathogens.

Germicidal teat dip in a herd with low prevalence of Streptococcus agalactiae and Staphylococcus aureus mastitis.

Effectiveness of an iodophor teat dip in reducing new intramammary infection and clinical mastitis was tested in a herd free of Streptococcus agalactiae and with a low prevalence of Staphylococcus aureus infections. In this 6-mo study with an average of 152 lactating cows on trial on sampling dates, right rear and left front teats were dipped after each milking while right front and left rear teats were undipped controls. Teat dipping significantly reduced new infections by Staphylococcus aureus, streptococci (other than Streptococcus agalactiae), coagulase-negative staphylococci, and Corynebacterium bovis and reduced clinical cases caused by infections established during the trial. However, the dip did not reduce new infections or clinical mastitis caused by coliform bacteria. Therefore, use of a germicidal dip is recommended for herds with a low prevalence of Streptococcus agalactiae and Staphylococcus aureus, but the practice should not be expected to control coliform mastitis.

Performance of dairy cows in midlactation fed high quality grass pasture and concentrate at three percents of energy requirements.

Thirty multiparous cows rotationally grazed high quality grass pastures (predominantly Dactylis glomerata and Poa pratensis) for 140 days. Stage of lactation was 54 to 192 days at beginning of trial. Cows were offered concentrates to supply 33, 66, or 100% of requirements for net energy for lactation above maintenance; daily intakes by the three groups averaged 3.5, 7.7, and 11.5 kg. Refusal of concentrate tended to increase with supplementation. Average milk production was 19.2, 20.4, and 21.5 kg. When individual yields were compared with an initial 2-wk period prior to trial, there was no difference in decline in milk flow, except for one 28-day period in midsummer when decline by the 33% group was greater than that by the 100% group. Milk fat yields were similar. Milk protein yields by the 100% group were significantly higher than those by the 33% group. Body weight changes were similar among groups. Quality of forage was high, and yields were adequate. Changes in milk flow attributable to movement of cows to fresh pastures were +1.35 kg per cow daily. Variations in in vitro dry matter disappearance, crude protein, and dry matter of forage were positively associated with changes in milk flow.

Feeding mastitic milk to calves: review.

Milk from cows treated with antibiotics for mastitis and other disorders has been fed to young calves in fresh or fermented form. Growth of calves so fed has been similar to that of control animals offered fermented colostrum or other liquid feeds. Incidence of health disorders in mastitis milk-fed calves has been no greater than in those fed control milks. Mastitic milk preserved by addition of propionic acid or formaldehyde was relatively unpalatable to the calves. Limited data indicate that first-lactation cows fed mastitic milk as calves suffered no more udder trouble than did their mates formerly given other liquid feeds.

Saturation in milk and meat fats.

Meat and milk products from ruminants (cows, goats, sheep, and beef animals) contribute 35 to 40 percent of the fat in the average American diet. Such fat is highly saturated, containing less than about 4 percent polyunsaturated fatty acids. The unsaturated plant lipids (fats) ordinarily consumed by the ruminant are hydrogenated (saturated) in the rumen. Transport and incorporation of this hydrogenated fat into meat and milk follows. Rumen hydrogenation does not take place until the fat is broken down to free fatty acids, thus establishing the fact that lipolysis is an essential feature of the process. Circumvention of this lipolysis may lead to more-unsaturated meat and milk fat.