The effect of strain of Holstein-Friesian, feeding system and parity on lactation curves characteristics of spring-calving dairy cows

The purpose of the present study was to investigate the influence of strain of Holstein-Friesian (HF) cow and feeding system (FS) on the lactation curve characteristics of spring-calving cows. The Wilmink model was used to analyse the lactation curves. The three strains of HF cows compared were high production North American (HP), high durability North American (HD) and high Breeding Worth New Zealand (NZ). The three FS compared were a high milk output from pasture feed system (MP), a high concentrate feed system (HC) and a high stocking rate feed system (HS). A repeated measures model with a factorial arrangement of treatments was used to determine the influence of strain of HF, FS, parity and their interactions on the shape of the lactation curve. The curve was described based on yield at calving, the degree of ascendancy between calving and peak yield, and the persistency after peak yield. Analysis of the residuals indicated a good fit of the Wilmink curve to the data set. Strain of HF, FS, parity and the interaction of strain of HF with FS had significant effects on lactation curve characteristics. In all three FS, the HP strain achieved the highest milk production post-claving and peak yield, with the lowest persistency of lactation. In the HC system, milk production post-claving and at peak yield were higher for all three strains. Offering higher levels of concentrate supplementation to the HP strain on a pasture-based system improved their persistency of lactation. The highest persistency of lactation was achieved with NZ strain. The highest milk production post-claving and at peak and lowest persistency was achieved with third parity cows. The existence of strain by feed system interactions for lactation curve parameters clearly exhibits that the optimum system of production varies with strain of HF.     

Insemination with Sex Sorted Fresh Bovine Spermatozoa Processed in the Presence of Antioxidative Substances

Flow cytometrically sex sorted spermatozoa are reduced in their fertilizing capacity, particularly when stored either in cooling extender or after freezing in liquid nitrogen. So far, preservation methods for sorted spermatozoa have differed only marginally from procedures used for unsorted semen. In the present study, a TRIS extender was modified to balance major cell damage caused by the sorting process and by liquid storage of the sorted spermatozoa. The new extender, containing a combination of antioxidants (AO) and bovine serum albumin (BSA), significantly increased the lifespan and fertilizing capacity of sex sorted spermatozoa. No significant differences were observed between unsorted controls and sorted samples for motility and status of sperm membranes as tested by fluorescein-isothiocyanat-peanut agglutinin/propidium iodide (FITC-PNA/PI). Acrosome integrity of spermatozoa was significantly better when semen was stored at 15 degrees C for 24 and 48 h in an extender containing AO with or without BSA as compared with controls (p < 0.05). There were no significant differences, in pregnancy rates of heifers inseminated at a natural oestrus, between unsorted controls (16/24, 66.7%) and both sorted groups (AO + BSA: 18/31, 58.1% and AO-BSA: 12/22, 54.5%). Additionally, it was shown for the first time that artificial insemination (AI) with liquid sexed bull spermatozoa stored for 72 h after sorting can result in pregnancy rates similar to AI with non-sorted semen.     

Retained Functional Integrity of Bull Spermatozoa after Double Freezing and Thawing Using PureSperm® Density Gradient Centrifugation

The main aim of this study was to compare the motility and functional integrity of bull spermatozoa after single and double freezing and thawing. The viability and morphological integrity of spermatozoa selected by PureSperm density gradient centrifugation after cryopreservation of bovine semen in two commercial extenders (Experiment 1) and the function of bull spermatozoa before and after a second freezing and thawing assisted by PureSperm selection (Experiment 2) were examined. On average, 35.8 +/- 12.1% of sperm loaded onto the PureSperm density gradient were recovered after centrifugation. In Experiment 1, post-thaw motility and acrosome integrity were higher for spermatozoa frozen in Tris-egg yolk extender than in AndroMed, whether the assessments were made immediately after thawing [80.4 +/- 12.7 vs 47.6 +/- 19.0% motile and 78.8 +/- 8.3 vs 50.1 +/- 19.5% normal apical ridge (NAR), p < 0.05] or after preparation on the gradient (83.3 +/- 8.6 vs 69.4 +/- 15.9% motile and 89.5 +/- 7.2 vs 69.1 +/- 11.4% NAR, p < 0.05). For semen frozen in Tris-egg yolk extender, selection on the PureSperm gradient did not influence total motility but significantly improved the proportion of acrosome-intact spermatozoa. After the gradient, both the total motility and percentage of normal acrosomes increased for spermatozoa frozen in AndroMed (Minitüb Tiefenbach, Germany). In Experiment 2, there was no difference in sperm motility after the first and second freeze-thawing (82.9 +/- 12.7 vs 68.8 +/- 18.7%). However, the proportion of acrosome-intact spermatozoa was significantly improved by selection through the PureSperm gradient, whether measured by phase contrast microscopy (78.9 +/- 9.7 vs 90.4 +/- 4.0% NAR, p < 0.05) or flow cytometry (53.4 +/- 11.7 vs 76.3 +/- 6.0% viable acrosome-intact spermatozoa, p < 0.001). The improvement in the percentage of spermatozoa with normal acrosomes was maintained after resuspension in the cooling extender and cooling to 4 degrees C (88.2 +/- 6.2) and after re-freezing and thawing (83.6 +/- 6.56% NAR). However, flow cytometric assessment of the sperm membranes revealed a decline in the percentage of viable spermatozoa with intact membranes after the second freezing and thawing compared with after gradient centrifugation (76.3 +/- 6.0% vs 46.6 +/- 6.6%, p < 0.001) to levels equivalent to those obtained after the first round of freeze-thawing (53.4 +/- 11.7% viable acrosome-intact spermatozoa). Sperm movement characteristics assessed by computer-assisted analysis were unaffected in the population selected on the PureSperm gradients but declined after cooling of the selected and extended spermatozoa to 4 degrees C. There was no further change in these kinematic measurements after the cooled spermatozoa had undergone the second round of freeze-thawing. These results demonstrate that bull semen can be frozen and thawed, followed by a second freeze-thawing cycle of a population of spermatozoa selected by PureSperm, with retained motility and functional integrity. This points to the possibility of using double frozen spermatozoa in bovine artificial insemination programmes and to the potential benefits of PureSperm density gradient centrifugation for the application of cryopreserved bull spermatozoa to other biotechnological procedures such as flow cytometric sex sorting followed by re-freezing and thawing.     

Effects of rice‐straw and phosphorus application on production and emission of methane from tropical rice soil

Rice‐straw amendment increased methane production by 3‐fold over that of unamended control. Application of P as single superphosphate at 100 μg (g soil)^–1 inhibited methane (CH₄) production distinctly in flooded alluvial rice soil, in the absence more than in the presence of rice straw. CH₄ emission from rice plants (cv. IR72) from alluvial soil treated with single superphosphate as basal application, in the presence and absence of rice straw, and held under non‐flooded and flooded conditions showed distinct variations. CH₄ emission from non‐flooded soil amended with rice straw was high and almost similar to that of flooded soil without rice‐straw amendment. The cumulative CH₄ efflux was highest (1041 mg pot^–1) in rice‐straw‐amended flooded soil. Appreciable methanogenic reactions in rice‐straw‐amended soils were evident under both flooded and non‐flooded conditions. Rice‐straw application substantially altered the balance between total aerobic and anaerobic microorganisms even in non‐flooded soil. The mitigating effects of single‐superphosphate application or low‐moisture regime on CH₄ production and emission were almost nullified due to enhanced activities of methanogenic archaea in the presence of rice straw.