Assessment of the morphology of frozen-thawed bull sperm in relation to its cryopreservation for artificial insemination

The morphology of sperm in raw semen was compared with that of the live sperm in semen which had been frozen and thawed. The thawed semen was stained with 6-carboxyfluorescein diacetate and propidium iodide and examined by fluorescence microscopy; smears of the raw semen were stained with eosin and nigrosin. Thirty-four ejaculates from 24 bulls of various breeds were examined. There were fewer abnormal heads, detached heads, coiled tails and proximal cytoplasmic droplets/pseudodroplets in the thawed semen than in the raw semen, there was no change in the number of bent tails, but the number of distal cytoplasmic droplets/pseudodroplets increased. There were no significant differences in morphology between ejaculates which passed or failed the osmotic resistance test after thawing, but failed batches tended to have more distal cytoplasmic droplets/pseudodroplets.     

Identifying the value of pasture improvement using wholefarm modelling

The economic value of pasture improvement in a farming system in a Mediterranean-type environment is assessed using farm modelling. Bioeconomic modelling combined with sensitivity analysis is used to explore how new annual legume species may impact on farm profit and land use. If introduced on all suitable soils the new pastures lead to a 26% increase in farm profit with an additional 12% of farm area being switched into pasture to support more livestock. However, stocking rates decline slightly, the enterprise mix becomes less diversified and several rotational changes are required. If the new pastures are only introduced on particular soils then farm profit increases by a lesser percentage and the pathways to additional profit vary, with both the pasture area and stocking rate either increasing or decreasing. To extract maximum profit from pasture improvement on any particular land management unit often requires management changes on other land management units, apart from those on which pasture improvement initially takes place. The economic value of pasture improvement is found to depend on the portfolio of pastures available for improvement and the nature and mix of the farm’s land management units.     

Mid-piece length of spermatozoa in different cattle breeds and its relationship to fertility

Recently positive correlation has been found between oxygen consumption (ZO2) in bull spermatozoa and non-return rates and concluded that an increase in ZO2, characteristic of the freeze/thaw process, was possibly associated with mitochondrial membrane damage during this procedure: alternatively, sperm may be hyperactivated through the capacitation-like effects of freezing/thawing. We speculated that the morphology of spermatozoa may be associated with their rate of ZO2 and fertility: for example, sperm mid-piece length where mitochondria are located. Such a relationship has not been investigated before, particularly in context of commercial cattle breeding programmes and bull fertility characteristics. Sperm biometry was performed on ejaculates obtained from 34 bulls representing six breeds: Holstein (yearlings and mature), Friesian, Belgian Blue, Aberdeen Angus, Charolais and Limousin. Five ejaculates were collected from every bull and from each sample a semen smear was fixed and stained with eosin/nigrosin: the mid-piece length of 40 sperm with normal morphology was measured in every sample. Data were analysed by breed, age and within each bull. Significant differences (p<0.01) between ejaculates in 9/34 bulls was found, as well as differences (p<0.001) between individual bulls within the same breed. The average mid-piece length for Aberdeen Angus was 13.35 microm, for Belgian Blues and Limousin around 13.8 microm and for Charolais 13.68 microm: for dairy breeds such as Holstein and Friesian it was about 13.4 microm. The mean value of mid-piece length for breed was compared with their 49 day non-return rate; a negative correlation (r = -0.53) was found in black and white dairy breeds.     

Shearing during pregnancy — review of a policy to increase birthweight and survival of lambs in New Zealand pastoral farming systems

Over the past decade, lambing percentages have risen in conjunction with a rise in the percentage of multiple lambs born. Multiple-born lambs are smaller than their singleton counterparts and are particularly susceptible to starvation-exposure. Any technique that can increase the birthweight or thermoregulatory capability, or both, of otherwise lightweight lambs has the potential to substantially increase survival of multiple-born lambs.

In the United Kingdom under housed conditions, shearing during pregnancy has been shown to increase both the birthweight and thermoregulatory capability of newborn lambs. However, shearing during pregnancy under pastoral conditions has failed to consistently affect the newborn lamb’s thermoregulatory capability. In contrast, under New Zealand’s pastoral conditions shearing during pregnancy has been found to increase birthweight, but results have been inconsistent in both magnitude and birth-rank specificity. Increase in feed intake by the dam, types of shearing comb used and changes in gestation length do not explain the variation observed. When studies involving shearing during pregnancy are collated it becomes apparent that there are two criteria that must be met to achieve a birthweight response. Firstly, the dam must have the potential to respond and secondly, the dam must have the means to respond.

Any increase in lamb survival through shearing during pregnancy would be predominantly through an increase in birthweight of otherwise lightweight lambs. However, in the few studies conducted to date, an increase in birthweight has not resulted in a statistically significant increase in survival. For an increase in birthweight to have a positive effect on lamb survival, lambs must be otherwise destined to be born within a birthweight range in which survival rate is below optimum (<4.0 kg), and the increase in birthweight observed must move a significant proportion of otherwise lightweight lambs into a higher range of survival rate.     

Metabolic responses to mid-pregnancy shearing that are associated with a selective increase in the birth weight of twin lambs

Previous studies have shown that shearing pregnant ewes at mid- or late-pregnancy is associated with an increase in lamb birth weight. The present study was designed to investigate metabolic responses that may underlie this response. Single- and twin-bearing ewes were either unshorn or shorn at mid-pregnancy (Day 69 of pregnancy; P69), and insulin, glucose and epinephrine challenges were conducted on P109–111 and P132–134. Shearing increased the birth weight of twin lambs by over 1 kg (P < 0.001) without having any effect on singleton birth weight. This response was associated with a 10–20% reduction in the insulin response to a glucose challenge (P < 0.05) without a change in glucose clearance following either glucose or insulin challenges. The lipolytic response to epinephrine challenge increased as pregnancy progressed, but was not associated with the increased birth weight of twin lambs born to shorn ewes. By late pregnancy, a 25% reduction in maternal IGF-I concentration and a two- to threefold increase in maternal IGFBP-1 concentration (P < 0.05) associated with shearing were observed. The increase in lamb birth weight associated with mid-pregnancy shearing may have been associated with an increase in the non-insulin dependent uptake of glucose by the placental-fetal unit.     

Morphological defects of the acrosome in boar spermatozoa

Morphological examination of semen from 17 boars of five breeds showed the presence of acrosome defects in 11 boars from four breeds. Two distinct types were seen; 'knobbed' sperm (type 1), of which two forms were found to be present by electron microscopy, and an uneven swellling of part of the acrosome (type 2) whose contents consisted of cytoplasmic and membrane-like material. The incidence of 'knobbed' sperm ranged from 0.2 to 6.3 per cent. Type 2 abnormalities were seen in only two boars, at 0.66 and 1.33 per cent.