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The purpose of a differential stain is to colour the cells concerned in such a way that two populations can be distinguished from each other and from the background. This is certainly true of staining mixtures used to differentiate `live' and `dead' mammalian spermatozoa. In practice, the distinction is between eosinophilic and non-eosinophilic cells with a secondary stain (e.g. nigrosin) which appears only to provide a background.

The degree of background staining can be varied from none to intense by varying the concentration of the secondary stain. At very low concentration, the non-eosinophilic spermatozoa tend to merge with the background, their outline is difficult to distinguish clearly and, consequently, they may be overlooked in a count. As the concentration of the background stain is increased,

Summary.

Semen from boar, bull, ram, rabbit, reindeer and stallion was diluted in formol citrate or formol saline and stained with eosin—nigrosin. The proportion of eosinophilic spermatozoa did not differ from that in fresh semen after storage for 48 hr in the formol diluent at temperatures ranging from 4°C to 40°C. Some samples were kept for periods up to 3 weeks with very little increase in the proportion of eosinophilic spermatozoa.

Summary. A simple slide is described in which the base is a permeable membrane so that a suspension of spermatozoa (or other cells) may be examined under controlled conditions with a microscope. An objective method of assessing the motility of spermatozoa in undiluted or diluted semen from a wide variety of species including cattle, horse, pig, rabbit, rat and sheep is described. It is shown to be well correlated with other methods of assessing motility and also with the non-return rate obtained with frozen cattle semen.

Summary. Mares at different stages of the oestrous cycle were given a single intravenous injection of 0·5 mg synthetic Gn-RH.

The mean area of the induced LH peak was significantly less at mid-cycle (Day 10–11) than at any other time. The mean height of the LH peak above preinjection concentration was greater at late oestrus and early cycle (Day 5–6) than at mid-cycle and early oestrus. There were no significant differences in mean FSH responses. The LH:FSH ratio for both height and area of induced peaks was significantly less at mid-cycle than at other times of injection. These results suggest that one releasing hormone could cause the release of both FSH and LH in the normal cyclic mare.

Summary. The seminal plasma in sperm suspensions from boar, bull, rabbit, ram and stallion was replaced with simple defined media as completely as possible by a combination of centrifugation through Ficoll and dilution. After this process, motility declined and the cells showed a tendency to agglutinate and/or stick to glass. Varying the ionic strength of the medium had little effect upon these parameters but sperm motility was preserved better in the presence of serum albumin. When a number of purified proteins and other macromolecules were tested individually in this way for their motility-preserving ability, bovine or human serum albumin was consistently the most effective. Defatting the albumin or altering its nature by mild reduction, oxidation or alkylation had little detectable effect on its motility-preserving ability; the protein did not appear to be acting as a chelator of metal ions, for it could not be replaced by EDTA.

The response of the spermatozoa to replacement of seminal plasma varied between species: bull spermatozoa were particularly sensitive and serum albumin had little effect upon their subsequent motility.

Summary. A technique is described for the in-vivo determination of mammary gland size and gross composition in goats by using nuclear magnetic resonance imaging (MRI). The volume of test objects determined with MRI had an error of +0·4 ± 1·6% of the actual volume. In lactating goats the in-vivo MRI estimate of mammary parenchymal volume was significantly greater than, but highly significantly correlated with, the weight of parenchyma determined post mortem (for the whole udder, r = 0·88, P < 0·001; for individual glands, r = 0·85, P < 0·001), MRI-determined estimates of the volume of fluid within the mammary gland were within 1·2% of the volume of milk removed from the udders after imaging. The spin-lattice (T₁) relaxation time of the whole udder correlated closely with the volume of fluid within the udder. The T₁ relaxation time of parenchymal tissue measured in vivo did not differ significantly from that determined immediately after post-mortem excision.

Keywords: mammary gland; magnetic resonance imaging; methodology; goat; lactation

Summary. Mammary development and regression were measured in goats in vivo using magnetic resonance imaging (MRI). Measurements were made during the first and second cycles of pregnancy, lactation and involution.

In primiparous goats, an exponential pattern of growth was evident during gestation and for the first 2 weeks of lactation. Parenchyma volume correlated significantly with milk yield across goats during early lactation, and across stage of lactation within goats. Milking was discontinued in Week 26 of the first lactation. Involution was characterized by an initial accumulation of fluid (over 2 days) followed by reabsorption; parenchyma volume did not decrease significantly until the 3rd week of involution, which was also the time at which these goats were mated to start their second gestation. Their udders still contained significant quantities of fluid (40–60% of the gross volume), but parenchyma volume was also greater (by 4·7-fold) than in goats beginning their first gestation. By Week 15 of gestation there was no longer a parity difference in parenchyma; the udders of first-gestation goats had grown significantly, but those of second-gestation goats had not. Conversely, between gestation Week 15 and laction Week 2 mammary growth was significantly more rapid in the second cycle, such that the udder was larger at the start of the second lactation.

Keywords: mammogenesis; mammary gland; lactation; pregnancies; goats; MRI

Summary. Epididymal spermatozoa from bull, rabbit and ram were incubated in homologous epididymal plasma or seminal plasma in a buffered saline-based medium with or without serum albumin. The spermatozoa were either diluted directly into the medium or were washed first.

No effect of washing was observed on the subsequent reaction of the cells to the different media.

A considerable proportion of the populations of epididymal spermatozoa survived (i.e. continued to exhibit motility) for up to 22 h at 30°C in the simple saline-based medium. Initially epididymal plasma had a slight stimulatory effect on sperm motility in ram and bull but it had no effect on sperm survival in any of the 3 species. Seminal plasma stimulated motility markedly in ram initially, but in all 3 species seminal plasma was detrimental to survival: in ram even a 15-min exposure to the fluid reduced survival. Serum albumin also stimulated motility; it delayed, but did not prevent, the detrimental effect of seminal plasma, although it had no effect itself on survival.

The effects of epididymal plasma, seminal plasma and serum albumin on surface properties of epididymal spermatozoa, i.e. agglutination, sticking-to-glass and eosinophilia, were also noted. These varied between species and there was no correlation between these effects and the effects on motility and survival.