Effects of different additives on cattle feed intake and performance - a systematic review and meta-analysis.

In the last few years, there has been a growing interest in the use of natural feed additives in animal feed. These can be used as replacements for antibiotics, to alter rumen fermentation and increase feed efficiency in ruminants. Therefore, the objective of this study is to evaluate the effects of adding different feed additives in the diet of beef and dairy cattle on their performance, dry matter intake (DMI) and feed efficiency, through a systematic review followed by meta-analysis. The systematic review suggested 43 peer-reviewed publications, according to the pre-established criteria. In beef cattle, the ionophore antibiotics reduced the DMI, improved the feed efficiency without interfering in the average daily gain (ADG). Non-ionophore antibiotics and propolis extract increased the ADG. In dairy cattle, the ionophores, yeast-based additives, and enzyme additives increased the feed efficiency, DMI, and daily milk production (MY), respectively. Essential oil supplementation in beef and dairy cattle had no effect on the feed intake and animal performance. The systematic review and meta-analysis allowed us to conclude that different feed additives have different effects on cattle performance, however, our results suggest that there are a few gaps regarding their effects on animal performance.

Comparison of Serum Thyroid Hormone Levels in Green-winged Macaws (Ara chloropterus) Using Radio and Chemiluminescent Immunoassays.

This study compared the use of radioimmunoassay (RIA) and chemiluminescent immunoassay (CLIA) to measure serum thyroid hormone levels in green-winged macaws (Ara chloropterus). The sample group comprised 20 male and 13 female (n = 33) healthy, captive green-winged macaws of reproductive age but outside of breeding season. Mean free triiodothyronine (T3), total T3, and free thyroxine (T4) measured by CLIA and RIA corresponded to 5.11 and 5.08 pmol/L (3.33 and 3.31 pg/mL), 1.59 and 1.56 nmol/L (103.5 and 101.5 ng/dL), and 8.25 and 8.82 pmol/L (0.64 and 0.69 ng/dL), respectively. Mean total T4 by RIA corresponded to 6.29 nmol/L (0.49 µg/dL). Mean free T4 and thyroid-stimulating hormone (TSH) levels differed according to immunoassay method, with higher values measured by RIA compared with CLIA. Sex influence was statistically significant in immunoassay results only on free T3 levels. Free T3 levels measured by RIA were higher than levels measured by CLIA in male birds, but this difference was not found with the female bird samples. Conversely, free T3 levels measured by CLIA were higher in the female macaws compared with male birds. Comparative analysis of thyroid hormone measurements in this study revealed that RIA and CLIA are equivalent methods to measure free T4 and total T3 levels but not TSH levels. These findings support the use of CLIA for free T4 and total T3 level determinations in green-winged macaws. However, the CLIA kit used in this study provided invalid total T4 level results for the macaws sampled. Radioimmunoassay and CLIA were equally ineffective for determining TSH levels in this species.