Orelha de Elefante Mexicana (Opuntia stricta [Haw.] Haw.) spineless cactus as an option in crossbred dairy cattle diet

new genotype of spineless cactus is being used in the diets of dairy cattle that are raised in semi-arid regions. However, little is known about its nutritional value. This study aimed to evaluate the effects of replacing Miúda (Nopalea cochenillifera Salm Dyck) with Orelha de Elefante Mexicana (Opuntia stricta [Haw.] Haw.) spineless cactus, on nutrient intake and digestibility, milk yield and composition, feeding behaviour, microbial protein synthesis, nitrogen balance, and ruminal and blood parameters of dairy cows. Ten Girolando cows, 500 ± 51.6 kg bodyweight, were distributed in a double Latin square design 5 x 5. The treatments consisted of replacement levels of Miúda (MIU) by Orelha de Elefante Mexicana (OEM) at 0, 25, 50, 75, and 100%. The intake and digestibility of dry matter (DM) (14.38–12.95 kg d-1, 716.3–658.9 g d-1), organic matter (OM) (13.01–11.43 kg d-1, 747.8–704.8 g d-1), crude protein (CP) (2.02–1.61 kg d-1, 863.8–845.2 g d-1) and total digestible nutrients (TDN) (9.38–7.92 kg d-1) decreased linearly with the increase in replacement. Despite the decrease in intake and digestibility, the supply of nutrients was sufficient to maintain a milk yield of 12.5 kg d-1. The average daily weight gain decreased linearly with the increase in replacement, while protein microbial efficiency (g microbial CP kg-1 TDN intake; 91.24 to 127.44 g kg-1) increased linearly. Thus, OEM could replace 100% MIU in diets with 48% of spineless cactus, for crossbred lactating cows with 12.5 kg d-1 milk yield. Therefore, OEM is a viable new option for producing milk in smallholder livestock systems in semi-arid regions.Keywords: Alternative forage, milk yield, ruminal parameter, semi-arid, smallholder livestock syste

Water relations and photosynthesis as criteria for adequate irrigation management in 'Tahiti' lime trees

Irrigation scheduling based on soil moisture status is one of the most useful methods because of its practicality and low cost. The effects of available soil water depletion on evapotranspiration (ETc), transpiration (E), leaf water potential at predawn (psiP) and midday (psiM), stomatal conductance (gs) and net CO2 assimilation (A) in lime 'Tahiti' trees (Citrus latifolia) were evaluated to improve irrigation schedule and minimize water use without causing water stress. The trees were spaced 7 <FONT FACE=Symbol>&acute;</FONT> 4 m and drip-irrigated by four drippers with the available soil water content (AWC) depleted by suspension of irrigation (40 days). Leaf water potential was measured on a pressure chamber (psiP and psiM) and leaf gas exchange was measured by infrared gas analyzer (E, gs and A). Evapotranspiration was determined with the aid of weighing lysimeter. Water soil content and potential (psiS) were monitored with TDR probes and tensiometers, respectively, installed at 0.3, 0.6 and 0.9 m depths. Meteorological variables were monitored with an automatic weather station in the experimental area. The threshold AWC level for the onset of ETc decline was 43%, and 60% for gs, A, E and Y P. Also, psiP was more sensitive to AWC than psiM, and is therefore a better tool for irrigation. When AWC was around 60%, values of psiP and psis were -0.62 MPa and -48.8 kPa, respectively