A summary of work conducted by AgResearch and reported in March 2011
Rising two-year cross-bred heifers – representative of typical dairy stock - that received ad lib access to Crystalyx Forage Plus for 23 weeks (starting 8 weeks prior to the introduction of bulls), showed significantly higher conception rates and slightly earlier dates of conception than the control heifers, which did not receive Crystalyx.
In addition, supplemented stock showed significantly better blood selenium and blood magnesium levels, although there was no beneficial effect on the other minerals monitored. No significant differences in live-weight gain were noted between control and supplemented mobs.
Stock consumed Crystalyx Forage Plus at an average of 0.133 kg/day/heifer, and this appears to have been sufficient to confer improvements in reproductive efficiency.
The aim of this trial was to evaluate the effect of Crystalyx Forage Plus on the reproductive efficiency of rising two-year-old heifers.
The trial was conducted on a Waikato grazier farm running predominantly Friesian-cross stock. Rising two-year-old heifers were divided into four mobs, two of which received Crystalyx Forage Plus, and two of which acted as control groups. Pre-trial blood analysis revealed 19 of the 20 heifers tested were deficient in one or more of the major elements associated with fertility. All heifers received injections for vitamin B12 and selenium, and also received copper capsules. Stock in the test mobs received Crystalyx Forage Plus at a rate of 22.5 kg (1 tub) per 25 heifers, and were given ad lib access for 8 weeks prior to the introduction of the bulls (Jersey breed). Bulls were introduced on 3 October and removed on 29 December 2010. Heifers were pregnancy tested on 11 and 12 January those not pregnant were retested on 22 February. All freemartins were removed from the groups after pregnancy testing and were excluded from the final analysis. During the course of the trial stock were also monitored for blood mineral status and live-weight gain. Pasture quality was determined by herbage analysis; feed quantity was assessed weekly by pre- and post-grazing walks.
Pregnancy testing revealed that there were significant differences between the control and supplemented heifers. At the final pregnancy check, 100% of the 157 supplemented heifers were pregnant, whereas only 95% (155) of the 163 control heifers were pregnant. In addition, estimation of foetal ages at pregnancy diagnosis showed that the mean gestational age of the supplemented mob was 75.1 days, compared to 71.6 days for the control mob, although this was not statistically significant.
Figure 1: Heifers supplemented with Crystalyx Forage Plus showed statistically significant improvements in conception rates.
Figure 2: Crystalyx supplementation had a highly significant impact on blood selenium levels, but not on blood copper or vitamin B12 levels.
Figure 3: Supplemented stock had significantly higher blood magnesium levels at the end of the trial, compared to control stock; however, no differences were seen for calcium or phosphate levels.
Overall, there was no significant difference in live-weight gain between the control and supplemented mobs. Prolonged dry conditions resulted in poor pasture growth during the last month of the trial, sufficient to cause one of the supplemented mobs to lose weight. Despite this, these Crystalyx-supplemented stock still managed to maintain their pregnancies through the most critical period of gestation.
Although the anticipated live-weight gain of supplemented stock did not eventuate, improvements in conception rate and date were noted. Very wet spring conditions followed by a prolonged dry period resulted in diminishing and inadequate pasture fed through December and January, and this is likely to have impacted on live-weight gain statistics. The increase in blood selenium in the supplemented stock may assist with reproductive efficiency, and the significantly higher blood magnesium levels in this group may also help to protect against metabolic disorders, which is critical around calving.
The report noted, ‘During the pregnancy checks on 11 and 12 Jan 2011, some of the animals were showing signs of grass staggers and were difficult to handle in the yards. Grass staggers index was elevated in the pasture at the beginning of the trial but not later. Two observers commented that the supplemented [S] mobs were easier to manage and were not as nervous and jumpy as the control [C] mobs at time of pregnancy diagnosis.’ This may indicate that the Crystalyx had a protective effect against grass staggers, although this would require further study to validate.