Resistance of Holstein-Friesian cows to infestation by the cattle tick (Boophilus microplus).

In two experiments, the milk production of 59 Holstein-Friesian cows in mid lactation was measured over 1 week before artificial infestation with 2,500 or 5,000 Boophilus microplus larvae. Host resistance, the proportion of female ticks applied but not engorging was estimated from weekly counts of engorging female ticks of 4.5-8. 0mm long. Mean host resistance was 79 and 67% in two experiments. Host resistance was not significantly related to milk yield before infestation, to early pregnancy, or to parity. Culling the 10% of cattle with the least resistance to ticks would result in removal of 19-21% of ticks in a herd. The results suggest that selection to improve the existing low levels of resistance to B. microplus might be undertaken without compromising milk production. However, low levels of resistance among the cattle studied and difficulties in assessment of resistance are likely to limit the usefulness of selection within the Holstein-Friesian breed.

Evaluation of tickGARD(PLUS), a novel vaccine against Boophilus microplus, in lactating Holstein-Friesian cows.

The effects of vaccination with the Bm 86 vaccine TickGARD(PLUS) against infestation with cattle tick (Boophilus microplus) and of holding cattle on a feedpad until 09:00 hours after the morning milking was tested on 40 mid lactation Holstein cattle using a factorial design. Vaccination resulted in a 56% reduction in tick numbers in the field over one generation, and a 72% reduction in laboratory measures of the reproductive efficiency of ticks. The liveweight gain of vaccinated cattle over 27 weeks was 18.6 kg higher than that of controls, and vaccinated cattle tended to have lower somatic cell count in milk (SCC). There were no other significant differences in measures of production. Cattle kept on the feedpad after the morning milking carried 26% more ticks than those returned immediately to their paddocks.

Extent and economic effect of heat loads on dairy cattle production in Australia.

OBJECTIVE: To investigate the extent of heat load problems, caused by the combination of excessive temperature and humidity, in Holstein-Friesian cows in Australia. Also, to outline how milk production losses and consequent costs from this can be estimated and minimised. PROCEDURES: Long-term meteorological data for Australia were analysed to determine the distribution of hot conditions over space and time. Fifteen dairy production regions were identified for higher-resolution data analysis. Both the raw meteorological data and their integration into a temperature-humidity thermal index were compiled onto a computer program. This mapping software displays the distribution of climatic patterns, both Australia-wide and within the selected dairying regions. Graphical displays of the variation in historical records for 200 locations in the 15 dairying regions are also available. As a separate study, production data from research stations, on-farm trials and milk factory records were statistically analysed and correlated with the climatic indices, to estimate production losses due to hot conditions. RESULTS: Both milk yields and milk constituents declined with increases in the temperature-humidity index. The onset and rate of this decline are dependent on a number of factors, including location, level of production, adaptation, and management regime. These results have been integrated into a farm-level economic analysis for managers of dairy properties. CONCLUSION: By considering the historical patterns of hot conditions over time and space, along with expected production losses, managers of dairy farms can now conduct an economic evaluation of investment strategies to alleviate heat loads. These strategies include the provision of sprinklers, shade structures, or combinations of these.

Attitudes and practices of Queensland dairy farmers to the control of the cattle tick, Boophilus microplus.

OBJECTIVE: To determine practices for the control of cattle ticks on dairy farms in Queensland, the attitudes of farmers to tick infestations and to identify opportunities for and barriers against the introduction of non-chemical methods of tick control. DESIGN: A survey of 199 dairy farmers from tick-infested parts of Queensland was undertaken by 20 dairy advisers and stock inspectors from October 1996 to June 1997. The sample was a proportional, random selection of dairy farms from four regions. A personal interview was conducted with each farmer and answers to 134 questions were obtained. RESULTS AND CONCLUSIONS: Most farmers were not concerned by cattle ticks on their own farms, although they believed that ticks are important to the dairy industry. They were most concerned about the development of chemical resistance by cattle ticks. Inadequate facilities and lack of motivation appeared to be the factors most limiting to improving the methods of control. Most farmers claimed to have only small numbers of ticks at worst. Although a control program recommended by the Queensland Dairyfarmers' Organisation was well regarded by farmers, few had adopted it. Many farmers saw no need to implement a strategic control program.

Production effects of cattle tick (Boophilus microplus) infestation of high yielding dairy cows.

Forty mid-lactation Holstein-Friesian cows, 100% lot fed, were assigned to four groups for 15 weeks. Two groups of 10 cows were infested each week with a gradually increasing number of Boophilus microplus larvae, while the other two groups were maintained free of ticks. Milk yield and composition (including somatic cell count, SCC), liveweight, dry matter intake, packed cell volume (PCV) and total plasma protein (TPP) were measured throughout the 15 week period. By week 15, control cows produced 2.86 l more milk and 0.14 kg more butterfat each day and had gained 10.6 kg more liveweight than infested cows. Each engorging female tick was estimated to be responsible for the loss of 8.9 ml of daily mild production and 1.0 g of bodyweight over the trial period. Milk composition, PCV and TPP were not significantly affected by cattle tick infestation. The dry matter intake of control cows was 0.83 kg greater than infested cows in week 12.

Relationships among calving season, heat load, energy balance and postpartum ovulation of dairy cows in a subtropical environment.

The study was designed to examine the relationships among calving season, energy balance, temperature humidity index (THI), and postpartum ovulation in high producing cows in a subtropical environment. Holstein cows calving in a feedlot dairy in southeast Queensland during winter (n = 23) and summer (n = 21) were monitored during the first 9 weeks of lactation. Cows were weighed and blood samples collected twice weekly: plasma progesterone, plasma metabolites related to energy and mineral balance, and haematological measurements were performed. Milk production was measured, body condition score was estimated, and trans-rectal ultrasound examinations of the ovaries were each undertaken once a week. The interval between calving and first ovulation was significantly longer in cows calving in summer (22.8 vs. 17.6 days, P < 0.05). Interval from calving to the first postpartum ovulation (FOVL) was inversely related to the mean plasma glucose concentration for the first 9 weeks after calving (GLU): FOVL = 80.0-17.9GLU, (R2 = 0.25, P < 0.001). Plasma progesterone concentration during the life of the second corpus luteum after calving was negatively correlated with THI during the first 2 weeks after calving (r = 0.55, P < 0.001). Plasma glucose concentration (GLU) was negatively correlated with milk yield (MYD) and rectal temperature (RT), and positively correlated with plasma calcium concentration (Ca) according to the following regression equation. GLU = 33.1 - 0.02MYD + 0.91Ca - 0.48RT, (R2 = 0.58, P = 0.0001).