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The present study evaluated possible modulation of the buck effect by nutritional and metabolic cues during the transition to the breeding season in adult goats with divergent bodyweight (BW) and body condition (BCS) at 27°N. In mid-February, goats (Boer × Spanish, n = 32) were assigned to receive one of the following two experimental diets to fulfill different allowances of nutritional requirements: (1) 100% (n = 16; BW = 52.3 ± 1.5 kg, BCS = 1.6 ± 0.1 units; T-100) or (2) 150% (n = 16; BW = 60.9 ± 2.4 kg, BCS = 1.6 ± 0.1 units; T-150) from February to August. Blood samples were collected to analyse thyroxine (T4), triiodothyronine (T3), non-esterified fatty acids (NEFA), triglycerides (Tg) and progesterone (P4). Final BW and BCS favoured (P < 0.001) the T-150 group (74.9 ± 2.8 v. 56.3 ± 1.4 kg, and 4.4 ± 0.2 v. 1.9 ± 0.1 units, respectively). However, mean values for NEFA, Tg, T3 and T4 did not differ (P > 0.05) between the experimental groups. Thereafter, in early August, half of the does in each diet treatment were randomly selected for determining the response to the ‘male effect’ (WM), forming the following two treatment groups: (1) T-100-WM (n = 8), or (2) T-150-WM (n = 8); the remaining does formed two groups without male exposure (WOM), as follows: (3) T-100-WOM (n = 8) and (4) T-150-WOM (n = 8). To evaluate ovarian activity, blood samples were collected from all does on Days 2–4 during the 14-day period after the male exposure. On Day 12, all does exposed to males (16/16), irrespective of the nutritional treatment, depicted ovulatory activity, whereas only 3/16 (18.75%) T-WOM does did, indicating a significant (P < 0.001) difference between these treatment groups. The increased nutritional level of the T-150 group during the anoestrous season did not result in an early onset of ovulatory activity. Does demonstrated similar metabolic hormones and concentrations of blood metabolites between the two nutritional treatments (100 v. 150% of the nutritional requirements), suggesting a high physiological plasticity between the groups, stabilising their metabolism according to the nutritional history female goats faced, and generating similar reproductive outcomes. The male effect seems to be enough to induce oestrus during the late anoestrous season, irrespective of BCS and BW.

Tillandsia recurvata is an epiphyte that grows on the canopy of many trees in tropical and subtropical areas of America. The objective of this study was to evaluate the effect of partial or complete substitution of sorghum stubble with T. recurvata on liveweight change, metabolic profile, and complete blood count of goats fed increasing levels (0, 30, and 60%, dry matter basis) of T. recurvata. Thirty non-pregnant three-year-old, non-lactating, healthy mixed-breed goats, ten animals per treatment (T0, T30, and T60), were adapted to diets and facilities for 14 days (d-14). Blood samples were collected at d-15, 28, and 56. At the last phase of the trial (from days 67 on), control goats tended to gain more (p = 0.09) weight than their counterparts consuming T. recurvata. Plasma protein, glucose, triglycerides, calcium, and phosphorus concentrations did not differ among dietary treatments (p > 0.05). Dietary treatment influenced red blood cells (higher for T60; p < 0.01), white blood cells (higher for T30; p < 0.05), mean corpuscular volume (higher for T0; p < 0.001), and mean corpuscular hemoglobin concentration (higher for T0; p < 0.01), although not the rest of the blood variables (p > 0.05). The hematocrit percentage tended to be higher (p = 0.06) in T30 than T0 and T60. It was concluded that replacing sorghum stubble with T. recurvata did not modify the metabolic status and maintained live weight of goats. Nevertheless, the use of T. recurvata as feed for goats would improve the nutrition of these animals in the dry season compared to the current diet obtained from an arid rangeland, reducing production costs, and would alleviate the damage caused by this aggressive epiphyte to host trees.

El objetivo del presente estudio fue evaluar el efecto del Atriplex (Atriplex canescens) y nopal (Opuntia ficus indica) en la alimentación de cabras lactantes y la producción de leche durante la sequía. Durante los meses secos, entre mayo y agosto de 2005 y entre mayo y junio de 2006, se realizaron tres experimentos en la región semiárida de San Luis Potosí, México. En el primero, se probaron dos tratamientos: CO) mantenidas en confinamiento y alimentación controlada (n=10) y AT) mantenidas en pastoreo con Atriplex (n=10). En el segundo se aplicaron dos tratamientos: AT) Atriplex (n=5) y NP) Atriplex más nopal (n=5). En el tercero tres tratamientos: AT) Atriplex (n=5), NP-1,0) Atriplex más 1,0% de nopal (n=4) y NP-1,5) Atriplex más 1,5% de nopal (n=5). En el primer experimento las cabras mantuvieron su peso, pero la producción de leche se redujo al 30% bajo confinamiento y menos del 8,0% en Atriplex al final del experimento. En el segundo, las cabras perdieron peso, a pesar de que la producción inicial de leche fue menor de 300 g/d. Las alimentadas con Atriplex redujeron su producción a casi la mitad de la producción inicial, mientras que la inclusión de nopal mantuvo la producción relativamente estable. En el tercer experimento, las cabras alimentadas con Atriplex mantuvieron el peso corporal, pero después de siete semanas la producción de leche fue del 25% de la producción inicial, a pesar de que esta fue de apenas 300 g diarios. En cambio, en las cabras suplementadas con nopal, la producción sólo se redujo al 45 y 64% de la producción inicial. Estos resultados son importantes para los caprinocultores de la región semiárida de México, donde las cabras podrían mantener una buena condición corporal, además de una producción de 150 a 250 g diarios de leche durante la época crítica utilizando Atriplex y nopal.