Split ejaculates from four boars were frozen with a programmable freezing machine, in mini-(0.25 ml) and maxi-(5 ml) plastic straws with an extender at either acidic (6.3) or alkaline (7.4) pH. Glycerol (3%) was used as cryoprotectant. The freezing of the semen was monitored by way of thermocouples placed in the straws. Post-thaw motility and acrosome integrity were evaluated; the latter using phase contrast microscopy, eosin-nigrosin stain and electron microscopy. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws than in maxi-straws. For the mini-straws, the motility was better when semen was exposed to an acidic environment during freezing, but this beneficial effect of the low extracellular p H was not evident when maxi-straws were thawed. The motility of the spermatozoa diminished significantly during the thermoresistance test (0 h and 2 h time) at 37°C in a similar way for both straws and extracellular pH's. The freezing procedure, no matter the extracellular pH, did not cause major acrosomal damages, but significantly more normal apical ridges were present in the mini-straws than in the maxi-straws. This in vitro evaluation indicated that the freezing method employed was better for mini-than for maxi-straws since the freezing of the 5 ml volumes was not homogeneous, due to the large section area between the surface and the core of the straw.hygienic (HAMMITT and MARTIN, 1989). For practical reasons, a larger frozen volume (i. e.

Contents: For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post‐thaw motility and the acrosome intep'ty of semen from four boars frozen with a programmable freezin machine, in mini‐(0.25 ml), maxi‐(5 ml) plastic straws and in 10 × 5 cm PVC‐ or Teflon FEP‐plastic bags (0.35–0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5°C, at a rate of −3°C/min, to–6°C, it was held for 1 min at −6°C, and was followed by further drop to −100°C at a rate of −20°C/min, with subsequent storage in LN2. The bags had a much shorter freezing point plnteau, compared to the maxi‐straws. Post‐thaw sperm motility was significantly higher when semen was frozen in mini‐straws or in bags than in maxi‐straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini‐straws than in the maxi‐straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags.

Summary Pooled ejaculates from six fertile boars were frozen under controlled conditions in Teflon® FEP‐film plastic bags (5 ml) and maxi‐straws (2.5 ml) using 3 % glycerol as cryoprotectant. The percentages of both post‐thaw motility and normal apical ridges were significantly higher (P< 0.001) for the bags (54.5 and 75 %) than for the maxi‐straws (40.1 and 59.4 %) respectively. For evaluation of the in vivo fertilizing capacity of the frozen‐thawed spermatozoa, 26 gilts were inseminated once 24 h after the first observation of standing reflex in their second oestrus, with 5 ml of semen (containing 5 billion spermatozoa) reconstituted in 80 ml of BTS from either bags or maxi‐straws. Ova were recovered from the oviducts/uteri 2–4 days following insemination and examined for cleavage and sperm binding to the zona pellucida (ZP). Significantly higher rates (P < 0.02) of fertilized ova were found in the bag‐inseminated (75%) than in maxi‐straw inseminated gilts (63%); and similarly their ova had significantly more spermatozoa in the ZP, irrespective of whether they were fertilized or non‐fertilized. This study confirmed that the plastic bags are suitable and may be used for packaging single insemination doses of deep frozen boar semen for routine A. I. work.

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