Letters to the editor

Extract

In order to utilize spring growth efficiently under a system of grassland farming, a New Zealand dairy farmer endeavours to calve as many cows as possible within a four to six weeks' period. To maintain this calving pattern, herd members must conceive by 70 to 80 days after calving. Consequently normal postparturient uterine involution, together with a minimum of delay in the onset of ovarian activity and oestral cyclicity, is of vital importance. A study of these phenomena may be very rewarding in helping to achieve optimal reproductive efficiency.     

A study of the pattern of staphylococcal contamination of the udders of cows in a dairy herd

Abstract

Extract

The results of the 1965–6 New Zealand national mastitis survey (Anon., 1967 Anon Ann. Rep. Res. Div. N.Z. Dept. Agric. 1966–67 1967 77 78  [Google Scholar]) indicated that β-haemolytic staphylococci were the most common bacteria isolated from the milk of dairy cows. Effective control of β-haemolytic stapyhlococci on a national scaledepends ultimately upon an understanding of population changes of this organism within the cow and within the herd.     

Production of irrigated Trifolium repens L. under a cutting regime in the subtropical region of Gauteng,South Africa

Abstract

The productivity of Trifolium repens L. cv. Ladino, under irrigation in the subtropical region of Gauteng, South Africa, is unknown. The performance of T. repens was determined over five years (1981/1982 to 1985/1986), at two defoliation frequencies, four levels of nitrogen (0, 400, 800 and 1 600 kg N ha^?1 ‐ total applied over five years), and either the removal or recycling of harvested material. Frequent, compared to infrequent defoliation, resulted in higher dry matter (DM) yields from the second year onwards. Dry matter yields were positively affected by the recycling of material, compared to no recycling. A mean DM yield of 191 ha^?1 in the first year and 12 t ha^?1 in the final year, was obtained. The highest DM yields occurred during October for all years and lowest DM yields from January to March. The first and final year showed similar peaks (late October) and troughs (March till April). Crude protein (CP) content of the herbage was influenced more by frequency of defoliation than recycling of material, where the highest CP content in any year was obtained from frequent defoliation. Nitrogen fertiliser applied up to a total of 1 600 kg N ha^?1 over five years had no effect on either DM yield or crude protein content. This study has shown that T. repens could be a productive pasture for at least five years in the subtropical region of Gauteng, South Africa. Productivity and quality of T. repens were enhanced by a defoliation interval of less than five weeks and when soil high fertility was maintained by recycled plant material.     

Factors associated with development of ileal impaction in horses with surgical colic: 78 cases (1986-2000)

Deal impaction is prevalent in the south-eastern USA, where feeding of Coastal Bermuda hay has been implicated as a risk factor. Alternatively, infection with the tapeworm Anoplocephala perfoliata has been identified as a risk factor for ileal impaction in the UK. We hypothesised that feeding Coastal Bermuda hay and failure to administer routinely an anthelmintic with efficacy against tapeworms would place horses at risk of developing ileal impaction in the USA. Seventy-eight horses, with surgically confirmed ileal impaction and 100 horses admitted for colic that did not have an ileal impaction, were selected retrospectively for logistic regression analysis. Using odds ratios (OR) as an index of risk, feeding Coastal Bermuda hay (OR = 2.9) and failure to administer a pyrantel salt within 3 months of admission (OR = 3.1) placed horses at risk of development of ileal impaction. This study confirms the belief that feeding Coastal Bermuda hay places horses at risk of ileal impaction, although the quality of the hay may also play a role. Periodic administration of anthelmintics with efficacy against tapeworms should be considered to reduce risk of ileal impaction.     

经人工授精传播的猪病及其预防措施

猪人工授精技术（Artificial insemination,AI）已在集约化养猪生产国中得到了广泛应用。人工授精是一种将优秀基因引入母猪群中的非常有效的工具,并能够将疾病传播的风险降至最小。然而,受到病原体污染的精液对生产实际的危害是巨大的。在已经从公猪精液中检测到的微生物中,大部分是非致病性的,但有一些是有名的病原体,如猪繁殖与呼吸综合症病毒,这部分病原体能给养猪业造成重大的经济损失。精液受到微生物的污染可能是由于公猪全身性感染和/或泌尿生殖道感染所致,或可能发生在精液采集、处理和存储过程中。这会导致精液品质下降,胚胎或胎儿死亡,以及受体母猪的子宫内膜炎和全身性感染和/或发病。用于从精液中分离细菌和病毒的常规技术因受多种原因的影响并不总是能获得理想的结果,这些原因包括所用技术缺乏敏感性和检测速度慢、对检测结果难以进行解释。近年来,PCR技术得到了普遍的应用,它们具有很高的敏感性,能很快获得检测结果,并且适合对大样本的检测。防止通过人工授精传播疾病的最佳方法是使用无特定病原体的公猪、对它们及其精液进行定期检测以及维持极高的生物安全水平。其它方法则应该侧重于利用合适的抗菌剂对精液进行处理,以及重点减少在采集、处理和存储过程中精液所受到的污染。     

Evaluation of estimated genetic merit for carcass weight in beef cattle: Blood metabolites, carcass measurements, carcass composition and selected non-carcass components

In Ireland, a new beef genetic index has been developed. Growth rate is expressed as expected progeny difference for carcass weight (EPD_CWT) and is estimated on an across-breed basis. Cross-breeding of dairy cows with both Aberdeen Angus and Belgian Blue beef sires is widely practised. The objective of this study was to compare blood metabolites, slaughter traits and carcass composition of progeny from Holstein–Friesian dairy cows and Aberdeen Angus (AA), Belgian Blue (BB), Friesian (FR) and Holstein (HO) sires. The AA and BB sires were selected, within breed, to be of either high (H) or low (L) estimated genetic merit for carcass weight. A total of 170 male progeny from spring-calving cows and 42 sires (10 AA, 13 BB, 7 FR and 12 HO) were artificially reared indoors and managed together until the end of their second grazing season when they were assigned to either a Light (560 kg) or Heavy (620 kg) slaughter weight. Blood metabolite concentrations were measured six times throughout life and feed intake was recorded during the first and second winter. Carcass measurements and selected non-carcass components were recorded after slaughter and the right side of each carcass was dissected into lean, fat and bone. Differences in blood metabolite concentrations amongst genetic groups were negligible although there were some effects of the prevailing level of nutrition. M. longissimus area scaled for carcass weight was 0.220, 0.221, 0.260, 0.255, 0.212 and 0.208 (SE 0.004) cm²/kg for AAH, AAL, BBH, BBL, FR and HO, respectively. Carcass measurements scaled for carcass weight were greater for L, AA, HO and the dairy strains than for H, BB, FR and the beef breeds, respectively. There was no effect of estimated genetic merit for carcass weight on carcass composition. Statistically significant interactions between genetic merit and beef breed existed for some traits with the genetic merit effect largely evident for AA only. BB and the beef breeds had more lean, less fat and more high value lean in the carcass than AA and the dairy strains, respectively. It is concluded that genetic group had little effect on blood metabolite concentrations but there were some feeding level effects. Estimated genetic merit for carcass weight affected carcass weight, m. longissimus area and carcass measurements scaled for carcass weight but the effects were confined to AA. There were large effects of beef breed and dairy strain on carcass composition.     

Leukocyte counts in bronchoalveolar lavage fluid obtained from normal and Maedi–Visna‐infected sheep

Background: Bronchoalveolar lavage has proven helpful for the diagnosis of certain ovine diseases of the lungs. There is insufficient data concerning the leukocyte profile of bronchoalveolar lavage fluid (BALF) from MaediVisna infected sheep. Objective: The objective of this study was to assess the differential leukocyte profile of BALF associated with Maedi virus infection in sheep and to determine whether cytologic examination of BALF is an effective way to diagnose Maedi or determine the severity of lung lesions. Methods: BALF and serum samples were analyzed from 400 sheep. Sediment smears of bronchoalveolar lavage were stained with Diff‐Quik and examined microscopically to obtain a 200‐cell differential cell count. Serum was tested using a commercial kit for Maedi–Visna virus antibodies. Lung samples obtained at the time of slaughter were weighed and examined histologically. Results: Maedi‐infected sheep (n=267; seropositive with lung lesions) had a significantly higher percentage of lymphocytes and lower percentage of macrophages in BALF than normal sheep (n=133; seronegative and no lung lesions). These differences were significantly more severe in animals with advanced vs moderate lung lesions. Using classification trees, a cut‐off of 13.5% lymphocytes was predictive of Maedi infection and a cut‐off of 24.5% lymphocytes was predictive of advanced lung lesions. Conclusions: Cytologic examination of BALF is useful for the clinical diagnosis of Maedi in sheep and provides important information about the severity of the lung lesions.     

Diagnosis and surgical treatment of epidural neoplasms in two ataxic horses

Two cases of ataxia caused by epidural neoplasia diagnosed with myelography and histopathology are presented in this report. One horse was diagnosed with lymphohistiocytic lymphosarcoma and the other with haemangiosarcoma. In both cases, subtotal dorsal decompression was performed as part of their treatment protocol. One horse was subjected to euthanasia immediately after surgery; however, the other horse recovered well, with no gait abnormalities and a normal myelographic dye column seen at 6 months post surgery. Although both horses were ultimately subjected to euthanasia, subtotal dorsal decompression provides a potential surgical treatment for epidural neoplasia.