Nutritional and ecological evaluation of dairy farming systems based on concentrate feeding regimes in semi-arid environments of Jordan

The objective of this study was to evaluate the nutritional and ecological aspects of feeding systems practiced under semi-arid environments in Jordan. Nine dairy farms representing the different dairy farming systems were selected for this study. Feed samples (n=58), fecal samples (n=108), and milk samples (n=78) were collected from the farms and analysed for chemical composition. Feed samples were also analysed for metabolisable energy (ME) contents and in vitro organic matter digestibility according to Hohenheim-Feed-Test. Furthermore, fecal nitrogen concentration was determined to estimate in vivo organic matter digestibility. ME and nutrient intakes were calculated based on the farmer's estimate of dry matter intake and the analysed composition of the feed ingredients. ME and nutrient intakes were compared to recommended standard values for adequate supply of ME, utilizable crude protein, rumen undegradable crude protein (RUCP), phosphorus (P), and calcium (Ca). Technology Impact Policy Impact Calculation model complemented with a partial life cycle assessment model was used to estimate greenhouse gas emissions of milk production at farm gate. The model predicts CH₄, N₂O and CO₂ gases emitted either directly or indirectly. Average daily energy corrected milk yield (ECM) was 19kg and ranged between 11 and 27kg. The mean of ME intake of all farms was 184MJ/d with a range between 115 and 225MJ/d. Intake of RUCP was lower than the standard requirements in six farms ranging between 19 and 137g/d, was higher (32 and 93g/d) in two farms, and matched the requirements in one farm. P intake was higher than the requirements in all farms (mean oversupply=19g/d) and ranged between 3 and 30g/d. Ca intake was significantly below the requirements in small scale farms. Milk nitrogen efficiency N-_eff (milk N/intake N) varied between 19% and 28% and was mainly driven by the level of milk yield. Total CO₂ equivalent (CO₂ equ) emission ranged between 0.90 and 1.88kg CO₂/kg ECM milk, where the enteric and manure CH₄ contributed to 52% of the total CO₂ equ emissions, followed by the indirect emissions of N₂O and the direct emissions of CO₂ gases which comprises 17% and 15%, respectively, from total CO₂ equ emissions. Emissions per kg of milk were significantly driven by the level of milk production (r²=0.93) and of eDMI (r²=0.88), while the total emissions were not influenced by diet composition. A difference of 16kg ECM/d in milk yield, 9% in N-_eff and of 0.9kg CO₂ equ/kg in ECM milk observed between low and high yielding animals. To improve the nutritional status of the animals, protein requirements have to be met. Furthermore, low price by-products with a low carbon credit should be included in the diets to replace the high proportion of imported concentrate feeds and consequently improve the economic situation of dairy farms and mitigate CO₂ equ emissions.