-The live weight gain of cattle on tropical pastures is reviewed and found to be low and dependent on the length of the growing season. Supplements may be added to address the primary limiting nutrient, which, in the dry season, is crude protein. The response relationships of live weight gain to level of supplement (protein or energy) that have been developed for animals on pasture in Brazil and Australia have been compared and found to be very similar. This gives confidence in recommending a supplementation strategy for cattle on tropical pastures. Response in the wet season was very low and likely to be uneconomic compared with dry season supplementation. Supplementation is costly and should only be used as a last resort, but the strategy needs to be viewed in the context of a growth path to a defined market or slaughter weight. In Australia, high inputs in the first dry season are risky as subsequent compensatory growth can reduce or eliminate the weight advantage of a supplement. There is less financial risk in using supplements towards the end of the growth path. Growth paths can follow many forms and there is no need to maximise live weight gain in each period. Targeted supplements in the second dry season, leucaena based systems, other special-purpose pastures or crops, and feedlots offer the most economical way for cattle to meet market targets. The expected annual live weight gain and weaning weight are other major factors which determine the growth path, target market which can be achieved, and the level of intervention (supplements, legumes, feedlots, etc) which are required and when. Some recent results on growth paths in Australia are presented.

The objective of this study was to investigate the effect of diet crude protein (CP) content and metabolisable energy (ME) intake on skeletal growth and associated parameters of growing steers prior to and during compensatory growth in weight and catch-up growth in skeletal elongation. The experiment was a factorial design with two cattle genotypes [Brahman crossbred (BX, 178 ± 6 kg) and Holstein-Friesian (HF, 230 ± 34 kg)] and three nutritional treatments; high CP content and high ME intake (HCP-HME), high CP content and low ME intake (HCP-LME) and low CP content and low ME intake (LCP-LME) with the ME intake of HCP-LME matched to that of LCP-LME. Nutritional treatments were imposed over a 103 d period (Phase 1), and after this, all steers were offered ad libitum access to the HCP-HME nutritional treatment for 100 d (Phase 2). Steers fed the high CP content treatment with a low ME intake, showed higher hip height gain (P = 0.04), larger terminal hypertrophic chondrocytes (P = 0.02) and a higher concentration of total triiodothyronine in plasma (P = 0.01) than steers with the same ME intake of the low CP content treatment. In addition, the low CP treatment resulted in significant decreases in bone volume (P = 0.03), bone surface area (P = 0.03) and the concentration of bone-specific alkaline phosphatase in plasma (P < 0.001) compared to steers fed the HCP-HME treatment. A significant interaction between genotype and nutritional treatment existed for the concentration of thyroxine (T4) in plasma where HF steers fed LCP-LME had a lower T4 concentration in plasma (P = 0.05) than BX steers. All steers with a restricted ME intake during Phase 1 demonstrated compensatory growth during Phase 2. However, HF steers fed the LCP treatment during Phase 1 showed a tendency (P = 0.07) for a greater LWG during Phase 2 without any increase in dry matter intake. Results observed at the growth plate and hip height growth suggest that catch-up growth in cattle may also be explained by the growth plate senescence hypothesis. Contrary to our initial hypothesis, the results demonstrate that greater CP intake during ME restriction does not increase compensatory gain in cattle during re-alimentation.

Spittlebugs are the main pest of tropical pastures and Marandu palisade grass (Urochloa brizantha cv. Marandu) is the most representative cultivated pasture in the tropics. Our objective was to characterize Marandu palisade grass responses subjected to Mahanarva (Hemiptera: Cercopidae) attack and to estimate the losses in terms of beef production from pasture-based systems. A set of five experiments were carried out. Three consecutive years of monitoring showed that Mahanarva spittlebugs increased their abundance after first rains with three to four peaks throughout the wet season. A decrease of 66% on herbage yield was observed in the greenhouse trial, with an average decrease of 61% on pools of calcium, magnesium, phosphorus, sulfur, potassium, crude protein, neutral-detergent fiber and in vitro digestible dry matter of Marandu palisade grass. Results from field experiments corroborated with greenhouse trial showing decreases on herbage yield varying from 31 to 43% depending on level of fertilization and grazing severity of Marandu palisade grass. Finally, an unprecedented 154-ha field experiment indicated that Mahanarva decreases 74% the beef productivity (i.e. kg body weight ha −1) of Nellore heifers grazing Marandu palisade grass. Brazil has the largest commercial beef cattle herd and is one of the top beef exporters in the world 1. Brazilian beef represents 20% of all global beef trading and, together with other agricultural commodities, it sums to about 21% of gross domestic product in Brazil 2. Beef cattle production in Brazil is characterized by pasture-based systems of which almost 90% of the cattle slaughtered comes from 3. However, despite highly representative, pasture-based livestock systems are extensive and conducted with low technology inputs resulting in low stocking rates (SR) and animal performance (i.e. average daily gain, ADG). Studies have reported beef production greater than 1,500 kg of body weight (BW) ha year −1 whilst the Brazilian average is much lower at about 150 kg BW ha year −14. Many factors stand out as key drivers for this poor productivity, among them: inadequate grazing management strategies, low soil fertility, and pest damage 5. The 215 million head of cattle in Brazil occupy approximately 160 million hectares composed by 70% of cultivated pasture species and 30% of native grasslands 6,7. Marandu palisade grass {Brachiaria brizantha (Hochst. ex A. Rich.) R. D. Webster [syn. Urochloa brizantha (A. Rich.) Stapf]} is the most representative of the cultivated pasture species, grown in about 50 million hectares in the country 8. It was launched by Embrapa in 1984 as an alternative to signal grass (Brachiaria decumbens cv. Basilisk, syn. Urochloa decumbens Stapf R.D. Webster) owing to its higher herbage yield and, mainly because of its resistance to "pasture spittlebugs" such as Notozulia entreriana (Berg, 1879), Deois flavopicta (Stål, 1854) and Deois schach (Fabricius, 1787) (Hemiptera: Cercopidae) 9. However, from the mid-1990s, spittlebugs from the genus Mahanarva have been r...

This study investigated the effect of five post-weaning supplementation strategies and two weaning weight groups on long-term growth, puberty and pregnancy percentage of Brahman crossbred heifers. Early-weaned (118 ± 6 kg liveweight) and normally-weaned (183 ± 6 kg liveweight) heifers were allocated to group pens (n = 4 and n = 5/pen for early- and normally-weaned respectively) and offered one of five levels of post-weaning protein supplementation: 0, 1, 2.5, 5 and 10 g of supplement/kg liveweight.day with ad libitum access to a low quality sabi grass (Urochloa mosambicensis) hay during the first dry season (169 days) after weaning. After the post-weaning supplementation period, all heifers grazed the same pastures as a single mob until the end of the experiment and were exposed to fertile bulls from January to May 2016. During the first dry season, supplement intake had a positive linear effect on liveweight gain and hip width gain with no difference in the response between weaning groups. Overall, heifers with higher supplement intakes (i.e. 5 and 10 g/kg) had higher hip height gain (P < 0.005), hip width gain (P < 0.001), body condition score (P < 0.001), and concentration of insulin-like growth factor-1 (P = 0.001), triiodothyronine (P = 0.04) and insulin (P = 0.05) in plasma compared to unsupplemented heifers. These changes resulted in thicker proliferative and hypertrophic zones (both P = 0.03) of the tuber coxae growth plate, larger diameter of terminal hypertrophic chondrocytes (both P = 0.004) at the end of the post-weaning supplementation period when comparing the highest level of supplementation with unsupplemented group. Unsupplemented heifers from both weaning weight groups demonstrated compensatory liveweight gain over the first wet season while evidence of catch-up growth in skeletal dimensions was observed in the second wet season. The main determining factor for pregnancy status of two-year-old Brahman crossbred heifers was pre-mating liveweight (P < 0.001), the pre-mating liveweight was in turn affected by post-weaning supplementation (P = 0.02) or weaning weight group (P < 0.001). This study further demonstrated the positive relationship between premating weight and the occurrence of pregnancy, with an approximate 300 kg pre-mating liveweight required to achieve approximately 80% (67.1–90.3% for a 95% confidence interval) probability of pregnancy in two-year-old Brahman crossbred heifers mated for 4 months.