Results show how goats are able to make use of limited feed resources that do not compete with human food, and transformed these into products of high nutritional and economic value as milk.
Milk yield and composition
Charpentier and Delagarde (2018) recommended access to pasture for 6 to 8 h/day. Therefore, access to the grazing plots in the experiment herein reported (8 h/day) was within recommended times by these authors. Livestock production systems on natural grasslands are a viable option for sustainable production given the lower use of fertilizers and seed that sown pastures require; plus promoting the use of local forage resources, within the context of agroclimatic conditions, favouring biodiversity (Morand-Fehr et al., 2007).
Results in Table 2 show how moderate milk yields in dairy goats may be sustained under different grazing regimes; although there was a trend (P=0.08) for higher yields under SPR grazing than under AAL, which became a highly significant difference (P<0.01) when milk was expressed as fat and protein corrected milk (FPCM).
Charpentier and Delagarde (2018) reported similar milk yields from Alpine dairy goats under grazing of temperate pastures during spring in France; and in northern Mexico, Escareño-Sánchez et al. (2011) reported from Criollo or Saanen dairy goats grazing arid grasslands that milk yields were under 1.5 L/day. Both reports stated that increased access time to grazing may increase milk yields from increased herbage intake, especially when no supplement is provided, or low amounts of supplements are offered.
However, in the present work there were no effects of the type of concentrate detected on milk yields (P>0.05), even though concentrate supplements accounted for between 16 – 20 % of daily intake estimated at 1.2 to 1.5 kg DM/goat/day.
In terms of the diversity of plants on the two grazing plots (Table 1), Maldonado-Jaquez et al. (2017) mentioned that the chemical composition of plant species available for grazing does have a direct relationship with milk yield and composition. That was observed with the significant interaction (P<0.01) between grazing regime and concentrate type for milk fat content, with higher milk fat in the SPR plot and the HE concentrate; and milk protein content was also significantly higher (P<0.01) in SPR than in AAL.
These results indicated how the higher plant diversity in the SPR plot had a positive effect on milk composition. Increased milk fat content in SPR is consistent with reports on sheep, cows and goats (Morand-Fehr et al., 2007). Fibre content of the diet does influence milk fat content (Charpentier and Delagarde, 2018), so that the diversity of plant species in SPR, representing varying fibre sources, may explain the higher milk fat content in that grazing regime.
Milk protein content may be affected by energy intake and feed characteristics; as may be from higher forage intake, higher quality of forage, or a higher level of concentrate supplementation, which enables milk with a higher protein content. This was corroborated in the current experiment, where goats on the SPR treatment, with a higher crude protein content in herbage and browse, had significantly higher milk protein content.
Concentrate supplementation
Tinoco-Magaña et al. (2012) stated the need for concentrate supplementation to sustain milk production and to avoid liveweight loss in dairy goats that base their feeding on tropical forages. In the experiment herein reported, type of supplement only had a significant interaction (P<0.02 and P<0.01) with grazing regime for milk fat content, with higher contents in the HE concentrate treatment.
Chemical composition of feeds
The chemical composition of grasses was similar to reports in the literature (Ferrufino-Suárez et al., 2022). In terms of browse species, the cazahuate (Ipomea murucoides) Mila-Arango et al. (2014) evaluated. in the state of Oaxaca in south Mexico, two species of cazahuate (Ipomoea murucoides and Ipomoea pauciflora subsp. pauciflora), under extensive grazing conditions during the dry season. The chemical composition reported for this browse species was similar to findings in the present work.
Opuntia cacti are distributed all over Mexico and used both for human food and as feed for livestock. Cacti as forage are a source of water, energy, and vitamins during the dry season or in arid areas. The chemical composition herein reported for Opuntia cacti is similar to that reported by other authors as Díaz-Plascencia et al. (2012).
Plants as oreganillo (Torres-León et al., 2023) and pingüica (Navarro-Cortez et al., 2022) have been widely studied for their bioactive compounds as tannins, glycoalkaloids, polyphenols, and saponins. However, their chemical composition has not been analysed as forage sources for livestock.
The legumes shown in Table 1 have been studied in dry areas of Mexico as alternative forage sources for cattle, goats and sheep (Mellado, 2008). However, those studies have concentrated in studying the seeds or pods, dried, ground, and used as supplementary feeds for ruminants. Therefore, values in those reports are higher for crude protein and lower in fibre than the figures reported in Table 3.
There were no reports found on the chemical composition of leaves, flowers and pods in conjunction for each species; as are usually consumed by goats from these trees and shrubs (Martínez-Ruiz et al., 2022).
Economic analyses
The highest component of feeding costs in dairy goat production is concentrate supplementation (Sainz-Ramírez et al., 2023), as was the case in the present work where the concentrate with the higher proportion of bought-in compound commercial concentrate represented the highest feeding costs.
Reliance on external inputs makes dairy production systems economically vulnerable. López-Ridaura et al. (2021) reported that the reduced economic activities due to the COVID-19 pandemic affected the availability and costs of inputs like fertilizers, seeds, and feeds with price increases up to 30% in Mexico and Central America.
In that sense, Shikuku et al. (2016) emphasised the need to develop feeding strategies for livestock systems that improve productivity, with local quality forages. Treatment SPR with HE concentrate supplementation meets these criteria, as it improved milk fat and protein content with sustained yields, and with a lower supplementation cost.
It is important to undertake integral assessments that promote sustainable dairy goat production. A less expensive concentrates based on homegrown cereals (HE) resulted in higher milk fat and protein content, with a positive interaction under the SPR regime, and had lower costs and higher returns when compared to a more expensive concentrate with a higher protein content (concentrate HP).