Effect of trenbolone acetate, melengestrol acetate, and ractopamine hydrochloride on the growth performance of beef cattle

The effect of trenbolone acetate+estradiol implants (TBA), melengestrol acetate (MGA), and ractopamine hydrochloride+TBA (RAC+TBA) on growth performance and carcass characteristics in beef cattle (n=680; 279±10.1 kg) fed barley grain/corn silage was examined in a 4-yr study (4 pens/treatment/yr; 262 ±8 d feeding period). In the first 2 yrs, treatments were: 1) control heifers (H-CON; no growth promoters (GP), 2) TBA implanted heifers (H-TBA), 3) MGA heifers (H-MGA), 4) control steers (S-CON; no GP), and 5) TBA implanted steers (S-TBA). A sixth treatment 6) RAC+TBA steers (RAC+TBA) was included in yrs 3 and 4. Overall DMI of heifers was increased (P<0.001) by TBA, but not MGA. Compared to H-CONs, H-TBA had greater ADG (P <0.001), G:F (P < 0.001), and carcass weight (P < 0.001), whereas S-TBA had increased ADG (P < 0.001), G:F (P< 0.001), and carcass weight (P< 0.001) compared to S-CON. Compared to H-CON, H-MGA had increased (P< 0.01) ADG, G:F and carcass weight. The RAC+TBA had increased (P< 0.01) ADG and carcass weight (3.2%), but not G:F or DMI compared to S-TBA. This 4 yr study showed a consistent positive impact of growth-enhancing technologies on the performance of Canadian feedlot cattle.

173 Greenhouse gas emissions and land use associated with the removal of growth-enhancing technologies from backgrounding and finishing cattle in Canada: A case study

Greenhouse gas emissions from backgrounding and finishing cattle with and without the use of growth-enhancing technologies (GET) were estimated using a whole-farm model, Holos (www.agr.gc.ca/holos-ghg). Model inputs were obtained from a four-year performance study using heifers (H) and steers (S) with six treatments (n = 40 hd treatment-1 yr-1): 1) H control (HCon); 2) H implanted (HTBA); 3) H melengestrol acetate (HMGA); 4) S control (SCon); 5) S implanted (STBA); and 6) S implanted + ractopamine hydrochloride (SRAC; conducted in the last two years). All cattle were finished to achieve a consistent number of days on feed (DOF; n = 233 ± 8). Lighter finish weights were observed for HCon and SCon. As a result, DOF were adjusted (-1 to 65 d) to achieve the same final weight as GET-treated cattle. Total emissions (kg CO2e head-1) were greater for Hcon_AdjHTBA (2967 ± 183) and HCon_AdjHMGA (2766 ± 84), than HTBA (2897 ± 184) and HMGA (2730 ± 81). Similarly, total emissions (kg CO2e head-1) for SCon_AdjSTBA (3169 ± 192) and SCon_AdjSRAC (3252 ± 202) were greater than STBA (2998 ± 153) and SRAC (3097 ± 185), respectively. On an intensity basis, (kg CO2e kg slaughter weight-1), emissions from GET-treated cattle [HTBA (4.49 ± 0.19), HMGA (4.39 ± 0.13), STBA (4.28 ± 0.17), and SRAC (4.31 ± 0.25)] were lower than HCon_AdjHTBA (4.60 ± 0.21), HCon_AdjHMGA (4.45 ± 0.18), SCon_AdjSTBA (4.52 ± 0.23), and SCon_AdjSRAC (4.52 ± 0.28), respectively. Furthermore, land-use (ha 100 kg slaughter weight-1) was reduced for GET-treated cattle (HTBA (0.068 ± 0.001), HMGA (0.067 ± 0.001), STBA (0.066 ± 0.001), and SRAC (0.067 ± 0.000)) compared to HCon_AdjTBA (0.071 ± 0.001), HCon_AdjMGA (0.069 ± 0.002), SCon_AdjTBA (0.072 ± 0.002), and SCon_AdjRAC (0.0073 ± 0.001), respectively. This study demonstrates that GETs can reduce the environmental footprint of beef cattle.

164 Effect of trenbolone acetate, melengestrol acetate, and ractopamine hydrochloride on growth performance of growing beef cattle

This study evaluated the effect of trenbolone acetate + estradiol implants (TBA), melengestrol acetate (MGA), and ractopamine hydrochloride (RAC) on the performance of beef cattle fed barley grain/corn silage diets. Beef cattle (279 ± 10.1 kg) were used in a complete randomized 4-yr study (yr 1, 2, n = 120 heifers and 80 steers; yr 3, 4, n = 120 heifers and 120 steers). Cattle were blocked by weight and randomly assigned to 4 pens/treatment/yr. Treatments were 1) control heifers [no growth promoters (GP)], 2) TBA implanted heifers, 3) MGA heifers, 4) control steers (no GP), and 5) TBA implanted steers (yrs 1 to 4), and included a sixth treatment 6) TBA implanted + RAC steers for yrs 3 and 4. Cattle were fed for a similar duration (262 d ± 8) in all treatments. TBA increased the DMI of steers and heifers (P &lt; 0.001) compared to controls (9.52 vs. 8.73 kg DM/d). MGA did not affect DMI (P = 0.41); however, TBA+RAC steers had grater DMI (P = 0.02; 9.91 vs. 9.58 kg DM/d) compared to TBA steers. Compared to controls, TBA heifers had greater ADG (P &lt; 0.001; 1.45 vs. 1.29 kg), G:F (P &lt; 0.001; 0.157 vs. 0.149), and carcass weight (P &lt; 0.001; 390 vs. 360 kg). TBA also increased steers ADG (P &lt; 0.001; 1.70 vs. 1.41 kg), G:F (P &lt; 0.001; 0.174 vs. 0.161), and carcass weight (P &lt; 0.001; 425 vs. 389 kg). Compared to control heifers, MGA increased (P &lt; 0.01) ADG, G:F, and carcass weight by 8.1%, 7.0%, and 4.7%, respectively. The ADG and carcass weight of TBA+RAC steers increased (P &lt; 0.01) by 5.6% and 3.2%, respectively with no effect (P = 0.87) on G:F compared to TBA steers. This 4-yr study demonstrates the consistent positive impact of conventional growth-enhancing technologies.

Reproductive efficiency Nellore and crossbred cows submitted to administration of melengestrol acetate (MGA) after FTAI protocols

This study aimed to evaluate the influence of medroxyprogesterone acetate (MGA) supplementation between the 13th and 20th day after Fixed-Time-Artificial Insemination (FTAI), on the conception and gestation rates of Nellore and crossbred cows (Nellore x Angus), pluriparous and lactating. For the study, 349 Nellore cows and 270 crossbred cows were selected, distributed into 1) group G1 (n=176): Nellore cows submitted to the FTAI protocol, without MGA supplementation; 2) group G2 (n=173): Nellore cows submitted to the FTAI protocol, with supplementation for 7 days of MGA® (0.28g/AU/day) from the 13th post-FTAI; 3) group G3 (n=119): crossbred cows: FTAI protocol, without MGA supplementation; 4) group G4 (n=151): crossbred cows: FTAI protocol followed by MGA supplementation for 7 days (0.28g/AU/day), from the 13th to the 20th day after FTAI. For statistical analysis, the procedures MIXED and GLIMMIX from SAS were used. G3 had higher rates of conception (CR=85.7%) and pregnancy (PR=95.8%) at the end of the breeding season (P<0.05), without the interference of supplementation with MGA (P>0.05). G1 females had a lower conception rate (TC=76.7%) (P<0.05), with the use of MGA® (CR-MGA=59.5%), but similar rates of pregnancy (PR=90.3%; PR-MGA=92.5%) to the G2, at the end of the breeding season (P>0.05). When G2 and G4 were compared, we found that crossbred females supplemented had higher rates of conception and pregnancy. In conclusion, crossbred animals have higher conception and pregnancy rates at the end of the breeding season. Besides, we found that Nellore females had a lower conception rate, with the use of MGA® Premix.

Toxicity of the pharmaceuticals finasteride and melengestrol acetate to benthic invertebrates

The toxicity of endocrinologically active pharmaceuticals finasteride (FIN) and melengestrol acetate (MGA) was assessed in freshwater mussels, including acute (48 h) aqueous tests with glochidia from Lampsilis siliquoidea, sub-chronic (14 days) sediment tests with gravid female Lampsilis fasciola, and chronic (28 days) sediment tests with juvenile L. siliquoidea, and in chronic (42 days) sediment tests with the amphipod Hyalella azteca and the mayfly Hexagenia spp. Finasteride was not toxic in acute aqueous tests with L. siliquoidea glochidia (up to 23 mg/L), whereas significant toxicity to survival and burial ability was detected in chronic sediment tests with juvenile L. siliquoidea (chronic value (ChV, the geometric mean of LOEC and NOEC) = 58 mg/kg (1 mg/L)). Amphipods (survival, growth, reproduction, and sex ratio) and mayflies (growth) were similarly sensitive (ChV = 58 mg/kg (1 mg/L)). Melengestrol acetate was acutely toxic to L. siliquoidea glochidia at 4 mg/L in aqueous tests; in sediment tests, mayflies were the most sensitive species, with significant growth effects observed at 37 mg/kg (0.25 mg/L) (ChV = 21 mg/kg (0.1 mg/L)). Exposure to sublethal concentrations of FIN and MGA had no effect on the (luring and filtering) behaviour of gravid L. fasciola, or the viability of their brooding glochidia. Based on the limited number of measured environmental concentrations of both chemicals, and their projected concentrations, no direct effects are expected by these compounds individually on the invertebrates tested. However, organisms are exposed to contaminant mixtures in the aquatic environment, and thus, the effects of FIN and MGA as components of these mixtures require further investigation.